Liquid-to-air membrane energy exchanger

ABSTRACT

An energy exchanger is provided. The exchanger includes a housing having a front and a back. A plurality of panels forming desiccant channels extend from the front to the back of the housing. Air channels are formed between adjacent panels. The air channels are configured to direct an air stream in a direction from the front of the housing to the back of the housing. A desiccant inlet is provided in flow communication with the desiccant channels. A desiccant outlet is provided in flow communication with the desiccant channels. The desiccant channels are configured to channel desiccant from the desiccant inlet to the desiccant outlet in at least one of a counter-flow or cross-flow direction with respect to the direction of the air stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. national stage entry of co-pendingInternational Application Number PCT/IB2011/002145 titled “Liquid-To-AirMembrane Energy Exchanger” filed Jun. 22, 2011 (published as WO2011/161547), which relates to and claims priority from U.S. ProvisionalPatent Application 61/358,321 titled “Liquid-to-air Membrane EnergyExchanger” filed Jun. 24, 2010, and U.S. Provisional Patent Application61/359,193 titled “System and Method for Energy Exchange” filed Jun. 28,2010. All of the applications noted above are hereby incorporated byreference in their entireties.

BACKGROUND OF THE INVENTION

The subject matter described herein relates generally to an energyexchange system for conditioning air in an enclosed structure, and moreparticularly, to a liquid-to-air membrane energy exchanger (LAMEE).

Enclosed structures, such as occupied buildings, factories and animalbarns, generally include an HVAC system for conditioning ventilatedand/or recirculated air in the structure. The HVAC system includes asupply air flow path and an exhaust air flow path. The supply air flowpath receives pre-conditioned air, for example outside air or outsideair mixed with re-circulated air, and channels and distributes the airinto the enclosed structure. The pre-conditioned air is conditioned bythe HVAC system to provide a desired temperature and humidity of supplyair discharged into the enclosed structure. The exhaust air flow pathdischarges air back to the environment outside the structure. Withoutenergy recovery, conditioning the supply air typically requires asignificant amount of auxiliary energy. This is especially true inenvironments having extreme outside air conditions that are muchdifferent than the required supply air temperature and humidity.Accordingly, energy exchange or recovery systems are typically used torecover energy from the exhaust air flow path. Energy recovered from airin the exhaust flow path is utilized to reduce the energy required tocondition the supply air.

Conventional energy exchange systems may utilize energy recovery devices(e.g. energy wheels and permeable plate exchangers) or heat exchangedevices (e.g. heat wheels, plate exchangers, heat-pipe exchangers andrun-around heat exchangers) positioned in both the supply air flow pathand the return air flow path. LAMEEs are fluidly coupled so that adesiccant liquid flows between the LAMEEs in a run-around loop, similarto run-around heat exchangers that typically use aqueous glycol as acoupling fluid. When the only auxiliary energy used for such a loop isfor desiccant liquid circulation pumps and external air-flow fans, therun-around system is referred to as a passive run-around membrane energyexchange (RAMEE) system, otherwise it is an active RAMEE system withcontrolled auxiliary heat and/or water inputs or extractions.

For the passive RAMEE system with one or more LAMEEs in each of theexhaust and supply air ducts, energy in the form of heat and water vaporis transferred between the LAMEEs in the supply and exhaust ducts, whichis interpreted as the transfer of sensible and latent energy between theexhaust air and the supply air. For example, the exhaust air LAMEE mayrecover heat and moisture from the exhaust air to transfer the heat andmoisture to the supply air during winter conditions to heat and humidifythe supply air. Conversely, during summer conditions, the supply airLAMEE may transfer heat and moisture from the supply air to the exhaustair to cool and dehumidify the supply air.

Laboratory prototype LAMEEs have been constructed and tested in passiveRAMEE loops to utilize both cross-flow and counter-flow arrangements foreach LAMEE. In a counter-flow configuration, the desiccant liquid flowsin a direction 180° away from the air flow direction in the adjacent airflow channel (i.e. counter-flow with respect to the air flow directionfor each pair of flow channels) and heat and water vapor are transferredthrough the semi-permeable, energy exchange, membrane of each LAMEE. Inthe cross-flow arrangement, the liquid desiccant in the LAMEE flows at90° or perpendicular to the air flow direction through each pair ofchannels in the LAMEE energy exchange membrane area.

Both counter-flow and cross-flow LAMEE devices can be used to recoverenergy from exhaust air-flows. This energy can be used to condition thesupply air using another LAMEE device. Cross-flow LAMEEs are not withoutdisadvantages. In certain circumstances, cross-flow exchangers generallyhave lower energy transfer effectiveness in comparison to counter-flowexchangers of the same energy exchange membrane area and inlet operatingconditions. Accordingly, it may be desirable to have an energy exchangesystem that utilizes counter-flow LAMEEs. However, counter-flow LAMEEsare generally more difficult and expensive to construct. In particular,counter-flow LAMEEs require headers positioned on each end of the LAMEEand require tighter design specifications. Accordingly, conventionalcounter-flow LAMEEs may be impractical for some applications but, wherehigher performance factors are needed, they may be cost effective forother applications.

Cross-flow and counter-flow LAMEE devices have been constructed andtested in laboratory RAMEE system loops. The laboratory test prototypesfor LAMEE devices have not performed as expected. In particular, thetest systems have not reached steady-state operating conditions during areasonable test period. Moreover, the internal geometry of the air andliquid flow channels are known to be far from the simple geometricconfigurations with uniform, equally distributed mass flow conditionsassumed in the reported theoretical models.

Several key problems exist with the past research and developmentefforts for LAMEE devices. First, simple theoretical models of RAMEE orHVAC systems containing LAMEE devices, with overly simplified internalgeometries and physics, fail to model what is physically occurringwithin the system. For example, each fluid flow will self adjust in afew seconds to distribute its local mass flux to minimize the pressuredrop across the exchanger as a whole unit for each type of fluid, flowchannel geometry, Reynolds number, Rayleigh number, and total mass flowrate. Within a fluid, both viscous flow forces and buoyancy forces canalter the flow streamlines. For example, buoyancy forces, caused byfluid density gradients, may result in unstable mal-distributed flowwhen the fluid density increases with height (i.e. counter to gravity)and the viscous forces are not sufficient to cause a uniform flow and soavoid a mal-distribution of flow within an exchanger. With some flowconfigurations in an exchanger, such flow conditions are likely to occurfor laminar liquid flows but not the air flows. The enhanced performanceof stable flows with enhancing buoyancy effects that self correctmal-distributions of flow are not exploited in existing systems.

When the self-adjusted flow is steady, the rate of entropy generationdue to viscous (laminar or turbulent) flow will be a minimum for eachflow channel and collectively for all the channels for each fluid (airor liquid desiccant) in the LAMEE. Due to small geometric variations anddestabilizing buoyancy effects in each channel and among all the flowchannels for each fluid, the self-adjusted flow distribution will not,in general, be such that the fluid mass flux is equally distributedamong all channels or is uniformly distributed in each channel for heatand mass transfer through the semi-permeable membrane surfaces in aLAMEE. In order to minimize the declination of performance of each LAMEEdue to the non-uniformities of flow distribution, the designspecifications must be very complete for each and all independentperformance influencing factors. When the uneven flow distribution leadsto unequal flows among channels and/or poor non-uniform area integratedor locally averaged heat and water vapor transfer rates, the flow ismal-distributed in the exchanger for energy exchange. Mal-distributionof flows in any LAMEE in a RAMEE system will cause the performance ofthe system to be sub-optimal. Mal-distribution of flow will beespecially prevalent for laminar flows with destabilizing buoyancyeffects within each liquid channel and among the many liquid flowchannels of a LAMEE. However, mal-distribution can also occur withtransition and turbulent flows. Local flow instabilities, due to channelflow surface geometry when the flow is above threshold Reynolds numbers,will induce local turbulent mixing that can reduce mal-distributed flowin each channel and will increase both the pressure drop and convectioncoefficients. Exploiting fluid flow turbulence instabilities forenhanced convection coefficients and reduction of flow mal-distributionin exchangers has not been fully recognized or exploited in HVACexchanger designs.

Further, LAMEE devices constructed with very flexible membranes needmore detailed design and construction specifications for each local flowregion in flow channels than more rigid flat-plate heat exchangers ifthey are to exceed the performance factors required for buildings {i.e.ASHRAE Std. 90.1 and 189.1} when tested using an accepted internationalstandard {i.e. ASHRAE Std. 84} and/or approach the theoreticalperformance factors put forward by modelers. There is no indication thatprevious researchers and inventors have fully understood thecomplexities of the physical problems or were aware of the large numberof independent design factors that influence the performance of theexchangers.

The key problems with existing RAMEE type energy recovery systems andHVAC systems having one or more LAMEE type devices for air conditioningsupply air for buildings are closely related to the research anddevelopment problems set forth above. Typically, the factors that impacton the performance are not considered as a complete set if they areconsidered at all.

The steady-state performance of a passive RAMEE system is notcharacterized by a single factor as are some simple systems (e.g. pumpsand motors). Rather, the performance may be characterized by a set ofsix dimensionless performance factors (i.e. four system effectivenessvalues for the measured fraction of the maximum possible steady-statesensible and latent energy transfer under summer and winter standardtest conditions and two RER values for the measured fraction ofauxiliary energy used with respect to the total energy transferredbetween the supply and exhaust air streams for the summer and wintertest conditions). The set of performance factors, Pf, can be referred toas the dependent objective dimensionless ratios determined by analyzingthe data from two standard steady-state tests for a passive RAMEEsystem.

The set of dimensionless ratios or factors that cause changes to thevalues in Pf are independent factors, If, because each one, orcollectively several or all, will, if changed significantly, change oneor more of the factors in the set, Pf. Mathematically, the relationshipis expressed such that the dependent dimensionless set Pf is only afunction of a predetermined dimensionless set, If, the operatingconditions for the inlet air temperature and humidity (i.e. one standardtest condition for winter and another for summer), and the uncertaintyin the measured test data for both Pf and If or in short Pf(If) andwhere the standard test conditions are constrained by steady-state orquasi-steady-state operating conditions for each test.

Existing LAMEE devices and passive RAMEE systems have not been designedto meet specified performance factors other than designing the LAMEEdevice with an internal geometry similar to flat plate heat exchangersconstructed using stiff elastic solids. That is, the systems have notmet the desired set Pf because not all the factors in the set If wereunderstood, considered, measured or specified.

A need remains to specify or predetermine a complete set of designparameters to construct a LAMEE and, for any inlet air conditions,select a narrow range of system operating conditions (i.e. the completeset If) if the RAMEE systems using two identical LAMEEs are to exceedall the required performance factors in the set Pf. When the designspecifications are complete, the set Pf for a passive RAMEE and its twoLAMEEs will be predictable in design, reproducible in manufacturing, andwith reproducible and certifiable steady-state standard test results.Another need remains for LAMEEs used in a passive RAMEE system having anincreased effectiveness. The LAMEEs need to be designed and operated tosatisfy conditions that are typical for conventional energy exchangesystems and that are required through international standards or localor state building codes.

SUMMARY OF THE INVENTION

In one embodiment, an energy exchanger is provided having a housingconstructed to meet a predetermined exchanger aspect ratio. A pluralityof panels extend through the housing. The panels have a semi-permeablemembrane forming an energy exchange area of the panel. The panels formdesiccant channels and air channels that are separated by thesemi-permeable membranes to facilitate contact between an air streamflowing through the air channels and desiccant flowing through thedesiccant channels within the energy exchange areas of the panels. Theenergy exchange area of each panel has a top and a bottom. A height ofthe energy exchange area is defined between the top and the bottom. Theenergy exchange area of each panel has a front and a back. A length ofthe energy exchange area is defined between the front and the back. Theexchanger aspect ratio is defined by the height of the energy exchangearea of each panel divided by the length of the energy exchange area ofeach panel. A desiccant inlet is provided in flow communication with thedesiccant channels. A desiccant outlet is provided in flow communicationwith the desiccant channels. The desiccant channels are configured tochannel the desiccant from the desiccant inlet to the desiccant outletin at least one of a counter-flow or cross-flow direction with respectto the direction of the air stream to facilitate heat and water vaportransfer through the semi-permeable membranes. The exchanger aspectratio is selected to provide at least one of a predetermined membranearea, a predetermined length, or a predetermine duration of exposure ofthe air stream to the desiccant.

In another embodiment, an energy exchanger is provided having a housing.A plurality of panels form desiccant channels and air channels thatextend through the housing. The air channels are configured to direct anair stream through the housing. The plurality of panels are spaced apartbased on a predetermined air to desiccant channel rates that defines anair channel width and a desiccant channel width. A desiccant inlet isprovided in flow communication with the desiccant channels. A desiccantoutlet is provided in flow communication with the desiccant channels.The desiccant channels are configured to channel desiccant from thedesiccant inlet to the desiccant outlet in at least one of acounter-flow or cross-flow direction with respect to the direction ofthe air stream to facilitate heat and water vapor transfer between thedesiccant in the desiccant channels and the air stream in the airchannels. The air to desiccant channel rates are selected to provide apredetermined mass or volume rate of air stream flowing through the airchannels and a predetermined mass or volume rate of desiccant flowingthrough the desiccant channels.

In another embodiment, an energy exchanger is provided having a housing.A plurality of panels form desiccant channels and air channels thatextend through the housing. The air channels are configured to direct anair stream through the housing. A desiccant inlet is provided in flowcommunication with the liquid desiccant channels. A desiccant outlet isprovided in flow communication with the liquid desiccant channels. Thedesiccant channels are configured to channel liquid desiccant from thedesiccant inlet to the desiccant outlet in at least one of acounter-flow or cross-flow direction with respect to the direction ofthe air stream. A semi-permeable membrane extends through each panel tofacilitate heat and water vapor transfer between the desiccant in thedesiccant channels and the air stream in the air channels. The airstream and the liquid desiccant pressure cause the semi-permeablemembrane to deflect during operation. The desiccant membrane is selectedbased on predetermined channel deflection ranges that are defined tolimit the amount of membrane deflection.

In another embodiment, an energy exchanger is provided having a housing.A plurality of panels form liquid desiccant channels and air channelsthat extend through the housing. The air channels are configured todirect an air stream through the housing. A desiccant inlet is in flowcommunication with the liquid desiccant channels. A desiccant outlet isin flow communication with the desiccant channels. The desiccantchannels are configured to channel desiccant from the desiccant inlet tothe desiccant outlet in at least one of a counter-flow or cross-flowdirection with respect to the direction of the air stream to facilitateheat and water vapor transfer between the desiccant in the desiccantchannels and the air stream in the air channels. The desiccant isselected based on predetermined salt solution concentration ranges for aselected life span and cost of the desiccant.

In another embodiment, an energy exchanger includes a housing. Aplurality of panels form desiccant channels that extend through thehousing. Each of the plurality of panels has a semi-permeable membranethat is selected to meet predetermined membrane resistance rangesdefining physical properties of the membrane. Air channels are formedbetween the desiccant channels. The air channels are configured todirect an air stream through the housing. A desiccant inlet is in flowcommunication with the desiccant channels. A desiccant outlet is in flowcommunication with the desiccant channels. The desiccant channels areconfigured to channel desiccant from the desiccant inlet to thedesiccant outlet so that the desiccant membranes facilitate heatexchange between the desiccant and the air stream. The membraneresistance ranges are selected to limit a flow of the desiccant throughthe desiccant membrane.

In another embodiment, an energy exchanger is provided having a housing.A plurality of panels form desiccant channels that extend through thehousing. The plurality of panels each have a desiccant membrane. Airchannels are formed between the desiccant channels. The air channels areconfigured to direct an air stream through the housing. The air streamflows through the air channels at a predetermined air flow ratio. Adesiccant inlet is in flow communication with the desiccant channels. Adesiccant outlet is in flow communication with the desiccant channels.The desiccant channels are configured to channel liquid desiccant fromthe desiccant inlet to the desiccant outlet so that the semi-permeablemembranes facilitate heat and water vapor exchange between the liquiddesiccant and air streams. The air mass flow rate ratio of the airstream selected to meet a predetermined exposure of the air stream tothe semi-permeable membranes.

In another embodiment, an energy exchanger is provided having a housing.A plurality of panels form desiccant channels extending through thehousing. Air channels are formed between adjacent desiccant channels.The air channels are configured to direct an air stream through thehousing. A desiccant inlet is in flow communication with the desiccantchannels. A desiccant outlet is in flow communication with the desiccantchannels. The desiccant channels are configured to channel desiccantfrom the desiccant inlet to the desiccant outlet so that the desiccantmembranes facilitate heat exchange between the desiccant and the airstream. The energy exchanger operates within predetermined exchangerperformance ratios that define a sensible and latent energy exchangebetween the desiccant and the air stream.

In another embodiment, a method of exchanging energy between a desiccantand an air stream is provided. The method includes extending a pluralityof panels through a housing of the energy exchanger to form desiccantchannels and air channels. A desiccant membrane is selected for each ofthe panels. An air stream is directed at a predetermined air flow ratiothrough the air channels. Desiccant is directed through the desiccantchannels. The desiccant membrane is selected based on membraneresistance ranges defined to limit a flow of the desiccant through thedesiccant membrane. The air flow ratio of the air stream is selected tomeet a predetermined exposure of the air stream to the desiccantmembrane. A flow rate of the desiccant with respect to a flow rate ofthe air stream is controlled to achieve predetermined exchangerperformance ratios that define a thermal energy exchange between thedesiccant and the air stream.

In another embodiment, a method of exchanging energy between a desiccantand an air stream is provided. The method includes extending a pluralityof panels through a housing of the energy exchanger. The plurality ofpanels are spaced based on predetermined air to desiccant channel ratesto form desiccant channels and air channels between adjacent panels. Thepredetermined air to desiccant channel mass or volume flow rates help todesign an air channel width and a desiccant channel width. A membrane isselected to extend through the panels based on predetermined channeldeflection ranges that are defined to limit an amount of membranedeflection with respect to the channel width. An air stream is directedthrough the air channels. A desiccant is directed through the liquiddesiccant channels in at least one of a counter-flow or cross-flowdirection with respect to the direction of the air stream so that themembrane facilitates heat and water vapor exchange between the liquiddesiccant in the desiccant channels and the air stream in the airchannels. The predetermined air to desiccant channel rates provide apredetermined volume rate of air stream flowing through the air channelsand a predetermined volume rate of liquid desiccant flowing through thedesiccant channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an energy exchange system formed inaccordance with an embodiment.

FIG. 2 is a side perspective view of a liquid-to-air membrane energyexchanger formed in accordance with an embodiment.

FIG. 3 a is a side perspective view of the liquid-to-air membrane energyexchanger shown in FIG. 2 having a cutout along the line 3-3 shown inFIG. 2

FIG. 3 b is a front view of the panels shown in FIG. 3 a.

FIG. 4 is a side perspective view of a liquid-to-air membrane energyexchanger panel formed in accordance with an embodiment.

FIG. 5 a is an exploded view of the panel shown in FIG. 4.

FIG. 5 b is a plan view of a screen and mounted or bonded flexible spaceflow guides for desiccant liquid flow channels formed in accordance withan embodiment.

FIG. 6 a is a view of an air channel formed in accordance with anembodiment.

FIG. 6 b is a front view of the air channels shown in FIG. 6 and beingdeformed.

FIG. 6 c is a front view of the air channels shown in FIG. 6 and beingdeformed.

FIG. 7 is a graph of mass flow rates as a ratio of the mass flow rate ofa desiccant with respect to a mass flow rate of air.

FIG. 8 is a graph of salt solution concentrations formed in accordancewith an embodiment.

FIG. 9 is a side perspective view of a liquid-to-air membrane energyexchanger formed in accordance with an alternative embodiment.

FIG. 10 is a side perspective view of a liquid-to-air membrane energyexchanger formed in accordance with an alternative embodiment.

FIG. 11 is a side perspective view of a liquid-to-air membrane energyexchanger formed in accordance with an alternative embodiment.

FIG. 12 is a side perspective view of a liquid-to-air membrane energyexchanger formed in accordance with an alternative embodiment.

FIG. 13 is a side perspective view of a liquid-to-air membrane energyexchanger formed in accordance with an alternative embodiment.

FIG. 14 is a schematic view of an alternative energy exchange systemformed in accordance with an embodiment.

FIG. 15 is a schematic view of another energy exchange system formed inaccordance with an alternative embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofcertain embodiments will be better understood when read in conjunctionwith the appended drawings. As used herein, an element or step recitedin the singular and proceeded with the word “a” or “an” should beunderstood as not excluding plural of said elements or steps, unlesssuch exclusion is explicitly stated. Furthermore, references to “oneembodiment” are not intended to be interpreted as excluding theexistence of additional embodiments that also incorporate the recitedfeatures. Moreover, unless explicitly stated to the contrary,embodiments “comprising” or “having” an element or a plurality ofelements having a particular property may include additional suchelements not having that property.

In one embodiment, a LAMEE energy exchanger is provided. Each embodimentwill represent at least one factor in the set If (presented below inTable 1 as independent factors G1-G10 and P1-P12). Many factors of theset If pertain to the LAMEE design and operation. Other factors pertainto the passive RAMEE system, comprising two identical LAMEEs, under astandard steady-state summer or winter test condition. The energyexchanger includes a housing having a front and a back and two sides.The housing has a top and a bottom extending between the front and theback. The housing is constructed to contain a set of air and liquiddesiccant flow channels which are each separated by a semi-permeablemembrane that permits heat and water vapor to be transferred between theair and liquid desiccant flows. Each of the flow channel energy exchangemembrane areas is rectangular in shape, with liquid desiccant floweither nearly counter-flow or cross-flow relative to the direction ofthe air flow in each adjacent fluid channel pair. Other predeterminedgeometric length ratios that may be specified for each LAMEE are theexchanger panel aspect ratio and liquid flow entrance/exit length ratio.The exchanger panel aspect ratio is defined by the height of each panelenergy exchange membrane area divided by the length of the energyexchange membrane area in the panel. A plurality of panels formingdesiccant liquid channels and air channels extend through the housing.The air channels are configured to direct an air stream uniformly, withequal mass flow rate among the total number of air channels in thehousing. Likewise, the fluid flow through each liquid flow channel isuniformly distributed in each liquid flow channel and the mass flow ratefor each channel is the same for all liquid flow channels. Inalternative embodiments, the air stream and the fluid flow through theheat exchanger may be non-uniform. A desiccant inlet is provided in flowcommunication with the liquid desiccant channels in the housing. Adesiccant outlet is provided in flow communication with the liquiddesiccant channels.

The design and operational parameters of the LAMEEs and passive RAMEEsystem will include all of the geometric (G) and physical (P) ratios setforth in Table 1.

TABLE 1 Defined Set of Dimensionless Independent Factors IF and theirRanges Parameter Description Suggested Range Parameter Meaning G1Counter or Cross 180° or 90° Dominant relative flow for the liquid flowdirections for desiccant and air air and liquid streams in eachdesiccant in each exchanger exchanger G2 Aspect ratio (AR = 0.1 < AR <3.0 Energy Exchange H/L) of each panel Aspect Ratio for in the LAMEE,each panel in a wherein AR is the LAMEE (Since this aspect ratio, H isthe ratio is also a factor height of the energy in reducing exchangearea in the buoyancy induced flow panel, and L is mal-distributions theair flow length effects the factor's of the energy magnitude may beexchange area of restricted.) the LAMEE G3 Inlet/outlet ratio 0.02 <Le/L < 0.2 ratio of the flow for primarily channel liquid counter-flowinlet/outlet length, LAMEE Le, divided by the 0.5 < Le/L < or = flowchannel length, L 1.0 for primarily cross-flow LAMEE G4 Ratio of the 0.0< sig(d_(w,air))/d_(w,air) < Air and liquid operating flow 0.2 desiccantchannel channel average 0.0 < sig(d_(w,liq))/d_(w,liq) < manufacturedand hydraulic diameter 0.2 operating width standard deviationcharacteristic for all channels variations causing [sig(d_(w,air)) andflow mal- sig(d_(w,liq)) for air and distributions due to liquidchannels] channel geometry with respect to the variations for eachaverage hydraulic LAMEE diameter for all air d_(w,air) and liquidd_(w,liq) channels (including membrane deflections) in a LAMEE G5 Ratioof the 0.0 < sig(d_(st))/d_(st) < Flow channel standard deviation 0.2variations in each of the flow channel typical flow channel hydraulicdiameter to reduce flow mal- to mean hydraulic distributions due todiameter for a geometric variations typical flow in a channel and sochannel in a make each LAMEE LAMEE for air or more compact in liquiddesiccant size G6 Ratio of the solid 0.05 < (Ass/Ast)_(air) < The screenarea surface area of (a) 0.2 ratios are (a) the air flow channel 0.1 <(Ass/Ast)_(liq) < directly proportional structural membrane .3 to thearea blockage support screen to its factor for the total area and (b)the membrane for water liquid flow channel vapor transfer and screensolid area to its (a&b) directly total area related to the turbulenceenhancement ratio for each flow G7 Support Spacer Dssa/Dsa = m/n anddistance between Ratios 0.3 < m/n < 5.0, the air channel where m and nare spacer support whole numbers structures in the average bulk flowstreamline direction, Dssa, divided by the distance between spacersupport structures normal to the average bulk flow spacer supportstructures, Dsa, is a fraction or whole number G8 Liquid flow liquidflow direction minimize mal- direction through the liquid distributioneffects flow channels is and maintain high controlled with performancefactors respect to the for the RAMEE direction of gravity system G9 Flowchannel angle 45 < Z_(g) < 135° angle Z_(g) between a vector normal tothe plane of each flow channel and the vector for the acceleration ofgravity G10 Flow channel edge 60 < O* < 120° angle O* between angle thevector parallel to the edge of each flow channel along its length andthe acceleration of gravity P1 Dimensionless flow _((a)) Re_(dh) >Re_(c) Where the characterization (b) Ra_(dh) < Ra_(c) characteristiclength numbers (a) is the hydraulic Reynolds number diameter (dh) and(Re) for each typical the subscript ‘c’ flow channel is such refers to(a) the that the flow is critical transition turbulent for the air fromlaminar to flow and, where turbulent flow and practical, for the (b) thecritical liquid flow channels transition from (b) Rayleigh stableuniform flow number (Ra) is to unstable mal- favorable for stabledistributed liquid uniform especially flow due to density when theliquid flow variations is laminar P2 Exchanger number 1.0 < NTU < 15Exchanger operating of transfer units condition (NTU) for heatcharacteristic ratio transfer during a to obtain a good RAMEE testexchanger and system effectiveness P3 Exchanger thermal 1.0 < Cr* < 10.0Exchanger operating capacity ratio (Cr*) condition during a RAMEEcharacteristic ratio test to obtain a good exchanger and systemeffectiveness P4 Ratio of the 0.1 < R_(m,wv)/R_(air,wv) < Membrane watermembrane water 3.0 vapor to air flow vapor resistance convection(R_(m,wv)) to resistance ratio to convective water obtain a good vapormass transfer exchanger and resistance (R_(air,wv)) system latent energyeffectiveness P5 Air flow pressure 10³ < p_(h)A_(c)/V_(c) < 10⁴ Air flowpressure drop ratio drop ratio for each LAMEE to obtain a goodperformance RER for the RAMEE system P6 flow channel ratio laminar flowchannel average of convective heat convective heat friction flowtransfer transfer coefficient, coefficients for coefficient, h h_(lam),at the same turbulent and channel Reynolds laminar flow, f and number is[1.1 < f_(lam), satisfy [f/f_(lam) < h/h_(lam) < 2.0]_(Re)h/h_(lam)]_(Re) P7 Air flow pressure p_(m,bt)/(rho * g * H) > 20Membrane liquid drop ratio (p_(h)A_(c)/V_(c)), penetration wherein p_(h)is the resistance pressure pressure drop across with respect to the theLAMEE in units maximum static of length, A_(c) is the pressuredifference area of the air in each LAMEE channel, and V_(c) is liquidflow channel the channel volume to prevent leaks in for air flow in thethe LAMEE during LAMEE normal operation P8 Membrane liquidp_(es,bt)/(rho * g * H) > 20 Membrane edge seal break-through liquidpenetration pressure ratio pressure with [p_(m,bt)/(rho * g * H)],respect to the static wherein p_(m,bt) is the liquid flow channelmembrane liquid in each LAMEE to break-through prevent leaks in thepressure, g is LAMEE under gravity, and H is the normal operation heightof the membrane panel energy exchange area P9 Elastic tensile yield 0.02< Membrane tensile limit ratio for the T_(m,yl)/(p_(l,op) * s_(ws)) <1.5 elastic yield limit membrane pressure per unit [T_(m,yl)/(p_(l,op) *s_(ws))], length with respect wherein T_(m,yl) is the to the supportscreen tensile yield limit pressure per unit for the membrane, length toreduce p_(l,op) is a typical membrane operating pressure defections onthe for the liquid in support screen for each LAMEE, and the membranes_(ws) is a wire spacing distance for a screen used to resist the liquidpressure for each liquid flow channel P10 Time duration for at_(salt,risk)/t_(op) < 0.15 Risk time duration risk of of salt solutioncrystallization in the crystallization salt solution over compared tothe the year divided by total time duration the total yearly time forRAMEE system duration of system operation to reduce operation(t_(salt,risk)/t_(op)) the relative time duration required for activecontrol to avoid crystallization in the RAMEE system P11 cost of salt orC_(salt,mix)/C_(LiCl) < 1.0 Salt solution cost mixture of salts usedcompared to the cost in the system of a lithium chloride divided by thesalt solution for the corresponding cost same RAMEE of LiCl for thesystem system P12 LAMEE heat 0.0 < Q_(sur)/Q_(exch) < LAMEE heatexchange rate 0.05 exchange rate with the surroundings (Q_(sur)) dividedby the heat rate transferred to or from the air flowing through theexchanger (Q_(exch)) during a standard test of a RAMEE system using twoidentical LAMEEs

With respect to factor G1, the desiccant channels are configured tochannel equally the liquid desiccant mass flow rate through each of theliquid flow channels from the desiccant inlet to the desiccant outlet inat least one of a counter-flow or cross-flow direction with respect tothe direction of the adjacent air streams to facilitate heat and watervapor transfer through the semi-permeable membrane between the liquiddesiccant flow in the desiccant channels and the air stream in the airchannels.

With respect to factor G2, the exchanger panel aspect ratio is selectedto provide a predetermined exposure through the semi-permeable membranebetween the air and liquid flow for adjacent channels in each LAMEE.

The liquid flow entrance/exit length ratio with respect to the length ofthe membrane energy transfer area (factor G3) may be utilized for flowchannels that are primarily counter-flow within a LAMEE. Theeffectiveness of the LAMEE may be partly determined using each of thefactors G1-G3. Accordingly, fluid flow direction (factor G1), aspectratio (factor G2) and entrance/exit flow length ratio (factor G3) in theset If may be used to partly determine the LAMEE performance.

With respect to the factor G3, for primarily counter-flow LAMEEexchangers, the ratio of the flow channel liquid inlet/outlet length,Le, divided by the flow channel length, L is approximately0.02<Le/L<0.2. For primarily cross-flow LAMEE exchangers, the ratio ofthe liquid flow inlet/outlet the ratio of the liquid flow channel inlet,Le, divided by the flow channel length, L is approximately 0.5<Le/L< or=1.0.

The determination of the statistical channel averaged hydraulic diametervariation for the liquid flow channels will be more difficult todetermine for the liquid flow channels than the air flow channelsbecause the volume flow rates and channel dimensions are small (e.g. 2to 10 times smaller than the air channels). The decrease in theeffectiveness due to mal-distribution of mass flows among the fluid flowchannels of each LAMEE in the passive RAMEE system, comprising twoidentical LAMEEs, will be partly determined using the ratio of standarddeviation of average channel hydraulic diameters to mean average channelhydraulic diameter (factor G4). For example, assuming a uniform flowthrough each channel but different flow rates among the set of channelsin a LAMEE for air flow through a large set of channels, with a standarddeviation of hydraulic diameter for the channels divided by the meanhydraulic diameter equal to 0.1 compared with one that has no variationsin the liquid flow channels, the decrease in air pressure drop acrossthe flow channels in a LAMEE relative to the same channels with no widthvariations will be about 3% for laminar flow and 6% for turbulent flowand the corresponding drop in RAMEE system effectiveness will be about6% for laminar flow and 8% for turbulent flow (it will be made clearthat laminar flows in the liquid channels may have strong destabilizingeffects unless the buoyancy forces re-stabilize the flows). If thevariations in flow channel widths are relatively identical for theliquid flow channels then the total decrease in the effectiveness forthe RAMEE system would be approximately 8.5% and 11% for laminar andturbulent flows, respectively. Variations in the channel widths for thetypical flow channels, characterized by factor G5, will further decreasethe system performance. Furthermore, since there may be a strongcorrelation between the liquid flow and air flow channel hydraulicdiameters (widths) (i.e. the variation in channel widths are notstatistically independent for each fluid), the drops in systemeffectiveness can be significantly larger. Furthermore, and as discussedbelow, mal-distribution of flow due to buoyancy effects in each liquidflow channel can result in an additional drop in effectiveness. Sincethe flow channel ratio of flow channel hydraulic diameters only dealswith the variations in the average flow channel hydraulic diameters,other independent parameters will be needed to complete the set If inTable 1.

Another embodiment is provided wherein the distance between themembranes of air and liquid flow channels (also called channel widths orhydraulic diameters) are designed to be nearly uniform over each channelin a LAMEE during typical operating conditions. Due to manufacturing andoperational tolerances, when averaged over each flow channel, thelocally averaged hydraulic diameter may be different for each fluid(i.e. air or liquid desiccant), for local flow regions within eachchannel and among all the channels in a LAMEE. Manufactured LAMEEs undertypical operating conditions will have a distribution of average channelhydraulic diameters that is statistically normal (i.e. Gaussian) ornearly normal in distribution considering the uncertainty bounds. Thevariation in channel average flow channel hydraulic diameters in a LAMEEwill cause air and liquid flow mal-distributions for each fluid amongthe many flow channels in each LAMEE. Consequently the energy transfereffectiveness and the fluid pressure drop of the LAMEE will be lowerthan that for an ideal theoretical design with equal mass flow rates foreach fluid channel. The variations among all the flow channel averagehydraulic diameters that cause variations in each fluid mass flow rateshould be designed to be small (i.e. the standard deviation of the flowchannel hydraulic diameters for both the air and liquid flow channelsshould be small with respect to the mean average flow channel hydraulicdiameter for each fluid within the LAMEE, G4). The flow channel averagehydraulic diameter variation in a LAMEE is also a factor forcounter-flow liquid channels because the pressure drop for the liquidflow entrance and exit regions in the channel may be a larger fractionof the total channel pressure drop and the flow path lengths may belonger (e.g. longer than the air flow path length through each channel).Channel width variations will be present for the typical air and liquidflow channels. Due to their normal distribution, these width variationswithin each panel are best characterized by their statistical propertiesas defined by geometric factor G5. In an exemplary embodiment a width ofthe air channels is selected based on a width of the desiccant channels.

As a summary of the geometric factors G6 to G10, the liquid channelscreen insures a minimum spacing for the channel width and enhances thetransition to turbulent flow for large liquid flow rates. The air andliquid flow channel screen area ratios (factor G6) is yet anotherpredetermined embodiment because the ratios are directly related toturbulence enhancement and blockage fraction of the membrane for watervapor transfer on the air side of the membrane. The air channel spacersupport structure ratio (factor G7) is another geometric embodiment thatassists the transition to turbulent flow and partly determines thegeometry of the flow channel through its structural supports. Factor G8defines the best liquid flow direction with respect to gravity througheach LAMEE exchanger which may be controlled to avoid liquid flowmal-distribution and factors G9 and G10 define LAMEE angles with respectto gravitational acceleration to get high performance factors for theRAMEE system and all its LAMEEs.

The new ratio of standard deviation for each liquid flow stream-tubehydraulic diameter in each liquid flow channel divided by the mean valuecan be used to analyze the decrease in expected effectiveness of eachLAMEE and the passive RAMEE system in which it is used or tested. Forexample, if the flow tube standard deviation ratio is 0.05 (i.e. 5%) forthe typical liquid flow channel in each identical LAMEE in the RAMEEsystem, then the decrease in total system effectiveness will be about 4%for turbulent flows but the loss of effectiveness may be much higher forlaminar liquid flows where the flow field is unstable due to buoyancyeffects.

Average or bulk mean flow streamlines in each of the air flow channelswill, depending on the air channel support structure, be on averagenearly parallel straight lines through the energy exchange area. The airflow channels are mostly a void region with parallel flow spacer guidestructures that cause the streamlines to be nearly straight while theinertial to viscous forces in the flow, characterized by the Reynoldsnumbers (i.e. Re_(dh)=Vd_(h)/k_(v) where V is the bulk mean channelfluid speed, d_(h) is the hydraulic diameter of the flow channel, andk_(v) is the kinematic viscosity of the fluid) are moderately high (i.e.300<Re_(dh,air)<1500 which, as will be discussed in more detail later,may be laminar or turbulent). This is not the case for the liquiddesiccant channels in counter/cross flow LAMEEs where the Reynoldsnumbers will be much lower and the flow is likely to be laminar at lowvalues of Cr*. The average liquid flow streamlines can be much morecomplex than for the channel flow of air because the liquid flowpassages cannot lead to parallel straight lines and when unstablebuoyancy forces are much greater than the viscous forces, characterizedby the Rayleigh number, Ra, they induce flow instabilities that causevery complex streamlines (i.e. Ra>Ra_(c)) for counter-flow exchangerswith parallel membranes (where Ra=−a*B*gd_(h) ²H²/(k_(v)t_(d)) where a*is the temperature gradient in the vertical direction (i.e. with respectto gravitational acceleration when the tilt angle is small), B* is thecoefficient of thermal expansion, g is the acceleration due to gravity,H is the vertical height of the flow channel and t_(d) is the thermaldiffusivity of the fluid). Since the viscous forces for turbulent flowsare much higher than they are for laminar flows, the critical Rayleighnumber, Ra_(c), at which buoyancy induced instabilities causesignificant flow mal-distributions changes significantly with the typeof flow. That is, the screens used in each fluid flow channel and thespacers used in the air flow channels can be used to enhance turbulencein each flow but, at the same time it is not desirable to unnecessarilyincrease the pressure drop due to each fluid flow. The preferred screensolid area to total screen area is given by factor G6. Even cross flowexchangers will have complex streamline patterns when Ra>Ra_(c) and sotheir performance factors will be lower than expected from theoreticalvalues derived from typical simplifying assumptions. Operating LAMEEexchangers so that the Rayleigh number is always in the stable flowregion (i.e. Ra_(dh)<Ra_(c)) allows the performance factors to be highcompared to exchangers that are not designed and operated to account forthe instability. The value for the critical Rayleigh number for aparticular exchanger is an empirical quantity that depends on theexchanger design and its fluid properties and Reynolds number.

With respect to the factor G7, the distance between the air channelspacer support structures in the average bulk flow streamline direction,Dssa, divided by the distance between spacer support structures normalto the average bulk flow spacer support structures, Dsa, is a fractionor whole number, such that Dssa/Dsa=m/n and 0.01<m/n<5.0, where m and nare whole or integer numbers.

With respect to factor G8, the liquid flow direction through the liquidflow channels is controlled with respect to the direction of gravity(i.e. from the bottom inlet to the top outlet for liquid flows that areheated within the channel and vice versa for liquid flows that arecooled in the channel) to minimize mal-distribution effects and maintainhigh performance factors for the RAMEE system.

With respect to factor G9, an angle Z_(g) between a vector normal to theplane of each flow channel and the vector for the acceleration ofgravity is such that 45<Z_(g)<135°. The angle Z_(g)=90° for mostapplications so that buoyancy effects will enhance the LAMEE performancewhen the correct flow direction is chosen for each exchanger.

With respect to factor G10, an angle O* between the vector parallel tothe edge of each flow channel along its length and the acceleration ofgravity is such that 60<O*<120°. This angle, or the LAMEE tilt angle(90°−O*), is normally selected to result in a positive enhancement ofperformance due to buoyancy effects.

Further embodiments are provided for with the flow channel flowconditions and their orientation, or combinations of several geometricand operational factors, for each LAMEE which involves flow fieldcharacterization through the Reynolds number and the flow stabilityfactor, Rayleigh number. The Rayleigh number can be selected to be mostfavorable by arranging the temperature gradients in each LAMEE to besuch that the fluid density always increases in the downward directionof gravitational acceleration. This implies that the flow channels in aLAMEE should be aligned so that their normal area vector is horizontaland the length vector of the flow channel is tilted with a large enoughangle to cause a favorable and significant density gradient for uniformflows in each channel and among all the channels. Channel flows in longthin channels with small or negligible entrance lengths for the flowsare well known to be one of: (a) fully developed laminar flow at lowReynolds number, (b) fully developed turbulent flow at high Reynoldsnumber, or (c) transition turbulent flows at intermediate Reynoldsnumbers between the two low and high transition Reynolds numbers. Theflow transition Reynolds number that causes the flow to transfer fromlaminar to transition turbulence tends to be fixed for any given channel(see factor P1) where the Rayleigh number indicates no buoyancy inducedmal-distributions (see factors G8, G9, & G10), but very small changes tothe surfaces inside each channel can cause large changes to thetransition Reynolds number. That is, the flow in a channel can becometurbulent when small increased surface roughness or flow separationswithin the channel flow changes are introduced at some low Reynoldsnumbers compared to laminar flow in the same channels with no roughnessadditions. In one embodiment, a characteristic Reynolds number for theair stream through the air channels is greater than a critical Reynoldsnumber for turbulent flow in the air channels. In another embodiment, acharacteristic Rayleigh number for desiccant flow in the desiccantchannels is less than a critical Rayleigh number for thermally inducedliquid density instability causing non-uniform mal-distributed flow at aReynolds number for desiccant flow.

The fluid inertial, viscous and buoyancy forces all play important rolesfor a well designed and operated LAMEE and their ratios arecharacterized by the Reynolds number and Rayleigh number in factor P1where it is stated that we prefer to have turbulent flow when practicaland we should always avoid adverse buoyancy effects in the liquid flows.The Reynolds number for the liquid flow through the liquid flow channelswill typically be very low (i.e. 0.1<Re_(dh,liq)<100). Under thesecircumstances, the liquid flow may be laminar for the lowest Reynoldsnumbers in the range but, for some specially designed internalgeometries the flow will become complex-laminar-turbulent or turbulentas the Reynolds number is increased from the low to the high end of thisReynolds number range. Therefore the liquid channel flow, which mayexhibit laminar flow mass flux channeling or fingering of the liquid forunfavorable Rayleigh numbers at the low Reynolds numbers in the aboverange, will, due to turbulent mixing, locally self adjust at higherReynolds number so that mal-distribution effects are much smaller. Onthe other hand, the air flow channels will most likely have turbulentflow, especially if some surface roughness is introduced to cause theflow to be turbulent. In an exemplary embodiment, the air channelsinclude turbulence enhancing surface roughness features to facilitateincreasing energy transfer that exceeds an additional air pressure dropenergy loss when convective heat and latent energy transfer increase. Inanother embodiment, the desiccant include turbulence enhancing surfaceroughness features when a Rayleigh number is less than a criticalRayleigh number at a Reynolds number for the flow.

Since the liquid is under a pressure greater than the adjacent channelair pressure, it causes the flexible semi-permeable membrane and itssupport structure in the air channel on either side of each liquid flowchannel to deflect or deform elastically. As previously noted, theliquid flow should be directed through each channel so that it minimizesflow mal-distributions (i.e. Ra<Ra_(c) for laminar flow and, when flowrates are higher, Re>Re_(c) for turbulent flow). The design andoperational conditions imply that the liquid flow direction will be suchthat the liquid flow will be from a bottom inlet to the top outlet forthe supply LAMEE exchanger and from the top inlet to the bottom outletfor the exhaust LAMEE exchanger for the standard summer test conditions.The flow directions through each LAMEE will be reversed for the winterstandard test conditions. That is, a liquid flow direction controllerwill be used so that the inlet direction will be bottom or top of eachLAMEE exchanger depending on the value of the Rayleigh number for eachexchanger and the angles of the flow channels with respect to theacceleration direction of gravity as defined in Table 1 for factors G9and G10. With these controlled liquid flow directions and a smallperformance enhancing tilt angle for the LAMEE, the problems of flowmal-distribution will have been reduced to a minimum for the geometricconfigurations of the flow channels and the channel Reynolds number. Infact, the restoring forces of favorable buoyancy forces that induce flowuniformity into the liquid flow channels that, due to flow channel widthvariations, can reduce the declination of performance factors for aLAMEE using factors G9 and G10 compared to the case of no restorativebuoyancy forces.

On the liquid flow side of the membrane, turbulent mixing within theflow channel may be a factor if there is a tendency toward laminar flowbuoyancy induced mass flux fingering at high Rayleigh numbers and verylow Reynolds numbers result in non-uniform exposure of the bulk flow tothe molecular diffusion transfer process in the liquid. In oneembodiment, for the factor P1, turbulence enhancement of the air andliquid flows through the LAMEE energy exchange channels is used toenhance turbulent transition and liquid flow directions are chosen foreach LAMEE operating condition to decrease buoyancy inducedinstabilities in the liquid flow channels. For a given flow channelgeometry, which is characterized by the hydraulic diameter and surfaceroughness, the Reynolds number is the only operating factor thatdetermines whether the flow is laminar or turbulent. The performanceeffectiveness and RER of the passive RAMEE and its LAMEEs will beenhanced with some turbulent mixing.

In other embodiments, an energy exchanger is provided. The exchangerincludes a housing for the air and liquid desiccant channels eachseparated by a semi-permeable membrane. A plurality of panels formingdesiccant channels and air channels extend through the housing. The airchannels are configured to direct an air stream through the housing. Theplurality of panels are spaced apart partly based on predetermined airto desiccant mass rates (P3) and the air channel width or spacing and adesiccant channel width or spacing. The air to desiccant mass flow ratemay be selected to achieve predetermined exchanger performance ratiosthat define a sensible and latent energy exchange rate between thedesiccant and the air stream. The panel spacing may also be dependent onfactors G4, G5, and P5. The air to desiccant mass flow rates may definean air channel width and/or a desiccant channel width. Theair-to-desiccant channel mass flow rates may be selected to provide apredetermined mass or volume of air stream flowing through the airchannels and/or a predetermined mass or volume of desiccant flowingthrough the desiccant channels. The desiccant channels may have anapproximately constant desiccant channel width. Additionally, the airchannels may have an approximately constant air channel width. In oneembodiment, a ratio of the average air channel width divided by theaverage desiccant channel width is within a range of 1 to 5.

A desiccant inlet header is provided in flow communication with all thedesiccant channels. A desiccant outlet is provided in flow communicationwith the desiccant channels. The desiccant channels are configured tochannel desiccant from the desiccant inlet to the desiccant outlet in atleast one of a counter-flow or cross-flow direction with respect to thedirection of the air stream to facilitate heat and water vapor transferbetween the desiccant in the desiccant channels and the air stream inthe air channels.

For a predetermined test condition of the passive RAMEE system, apredetermined equal mass flow rate of supply and exhaust air passthrough each identical LAMEE. By so doing, the number of transfer unitsfor heat transfer (NTU) in each LAMEE is predetermined (factor P2). Whenthe pumping rate of liquid desiccant is chosen, the heat capacity rateratio (i.e. the mass flow rate times the specific heat of desiccantliquid flow divided by the mass flow rate of air) through each LAMEE,Cr*, is predetermined (factor P3). There may be a trade-off for theselection of Cr* because increasing the liquid flow rate may enhanceturbulence in the liquid flow channels and will increase Cr*, which canhave positive and negative effects on the effectiveness. Accordingly,the value of Cr* should be selected so that the effectiveness of theLAMEE is a maximum when the highest performance is required.

Other embodiments for energy exchangers are provided. The exchangerincludes a housing containing the air and liquid flow channels eachseparated by a semi-permeable membrane. A plurality of panels formingdesiccant channels and air channels extend through the housing. The airchannels are configured to direct an air stream through the housing. Adesiccant inlet header is provided in flow communication with all thedesiccant channels. A desiccant outlet is provided in flow communicationwith the desiccant channels. The desiccant channels are configured tochannel liquid desiccant from the desiccant inlet to the desiccantoutlet in at least one of a counter-flow or cross-flow direction withrespect to the direction of the air stream. A semi-permeable membraneextends through each panel to facilitate heat and water vapor transferbetween the desiccant liquid in the desiccant channels and the airstream in the air channels. The membrane may be selected based onmembrane resistance ranges defined to reduce a flow of desiccant throughthe membrane. The semi-permeable membrane possesses a resistance towater vapor diffusion which, relative to the typical convection watervapor transport resistance in the air channels, lies within a specifiedrange given by factor P4. A water vapor transfer resistance ratio isdefined by a ratio of the membrane water vapor resistance (R_(m,wv)) toconvective water vapor mass transfer resistance (R_(air,wv)). The ratioof the membrane water vapor resistance (R_(m,wv)) to convective watervapor mass transfer resistance (R_(air,wv)) may be within a range of 0.2to 3.

The static air pressure drop as it passes from air inlet to outlet ineach LAMEE in a RAMEE system is the same for each air channel. The rangeof acceptable air pressure drops for a LAMEE so that the passive RAMEEsystem will have a high RER value in the set Pf is presented usingfactor P5. In one embodiment, the air flow pressure drop ratio isdefined as (p_(h)A_(c)/V_(c)), wherein p_(h) is a pressure drop of theair stream across the energy exchanger, A_(c) is an area of an airchannel, and V_(c) is a volume of the air channel. In one embodiment,the air flow pressure drop ratio is between 1×10³ and 1×10⁴.

With respect to factor P6, a flow channel ratio of convective heattransfer coefficient, h, (i.e. for turbulent flow) with respect to thetheoretical laminar flow convective heat transfer coefficient, h_(lam),at the same channel Reynolds number is [1.1<h/h_(lam)<2.0]_(Re). Thechannel average friction flow coefficients for turbulent and laminarflow, f and f_(lam), satisfy [f/f_(lam)<h/h_(lam)]_(Re).

Turbulent flows in channels with flow at a particular Reynolds numberwill have enhanced heat and mass transfer rates compared with those withlaminar flows. Taking advantage of this fact is the purpose of factorP6. Accordingly, the internal surface roughness may be enhanced forchannel flows that would have been laminar for smooth internal surfacesbut turbulent for the same channel with rough surfaces or flowseparation causing surfaces at the same Reynolds number (i.e. operatingclose to the flow transition Reynolds number between laminar andtransition turbulence so as to cause the laminar flow to becometurbulent). The heat or mass transfer enhancement is a factor for theair flow channels where the relatively high laminar flow characteristicconvection resistance dominates the total resistance and the design needfor the LAMEE energy exchange total area and LAMEE total volume andgeometry. Air channel support structures must be chosen and positionedto provide the desired membrane channel width and concurrently induce aturbulent flow transition from laminar to turbulent flow, but not causean excessive increase air pressure drop for the flow channel. The ratiosfor the same channel flow Reynolds number are empirically selected forenhanced heat and mass transfer coefficients compared to laminar flowheat and mass transfer coefficients, which may be large, while theratios for increased friction coefficients compared to laminar flowfriction coefficients may be smaller (i.e. there is a net heat and masstransfer benefit for the turbulence enhancement relative to the air flowpressure drop increase).

The semi-permeable membrane is designed (or selected) and operated toavoid the transfer of any liquid from the liquid channels to the airchannels. Factors P7 and P8 define the acceptable liquid pressure ratiosthat should be used for selecting the semi-permeable membrane and itsedge seals in each LAMEE.

The difference between the static desiccant liquid pressure and theadjacent static air pressure cause the semi-permeable membrane todeflect during normal operation and the deflections will, as discussedabove, result in a distribution of typical inter-channel hydraulicdiameters that decrease the LAMEE and RAMEE system effectiveness. Thedeflections of the semi-permeable membrane through its air side supportscreen will be determined using its elastic properties, the geometry ofthe screen pores, and the liquid pressure. The operating properties arecombined into a ratio (factor P9) that should be selected within aspecified range for the design and operation of each LAMER In oneembodiment, the membrane is selected based on a predetermined channeldeflection range that is defined to limit the amount of membranedeflection. A standard deviation of the hydraulic diameter of all of theair channels and desiccant channels divided by a mean value of ahydraulic diameter for one of the air channels or desiccant channels maybe within a range of 0.0 to 0.2. A standard deviation of a hydraulicdiameter for one air channel or desiccant channel divided by a meanhydraulic diameter for the air channel or desiccant channel may bewithin a range of 0.0 to 0.2.

In another embodiment, an energy exchanger is provided. The exchangerincludes a housing containing the air and liquid flow channels separatedby a semi-permeable membrane. A plurality of panels forming desiccantchannels and air channels extend through the housing. The air channelsare configured to direct an air stream through the housing air channels.A desiccant inlet is provided in flow communication with the desiccantliquid channels. A desiccant outlet is provided in flow communicationwith the desiccant liquid channels. The desiccant channels areconfigured to channel desiccant from the desiccant inlet to thedesiccant outlet in at least one of a counter-flow or cross-flowdirection with respect to the direction of the air stream to facilitateheat and water vapor transfer between the desiccant in the desiccantliquid channels and the air stream in the air channels. The liquiddesiccant salt concentration mixture is selected based on predeterminedsalt solution saturation concentration limit and membrane surface airside relative humidity for each climatic region in which the RAMEEsystem is to operate in applications. In one embodiment, the desiccantis selected based on at least one of an operating temperature orhumidity ratio of the air stream, wherein the humidity ratio is definedby a moisture to air content of the air stream. The annual time fractionduration of RAMEE system operation without the risk of saltcrystallization problems for a particular climatic region (factor P10)and the expected life-cycle costs relative to that for a system usingpure LiCl or LiBr for the system (factor P11) are partly based on thedesiccant selection. Each of the above embodiments (factors P10 and P11)are uniquely defined for the LAMEEs operating within a passive RAMEEsystem under steady-state test conditions.

With respect to factor P12, the LAMEE heat exchange rate with thesurroundings (Q_(sur)) divided by the heat rate transferred to or fromthe air flowing through the exchanger (Q_(exch)) during a standard testof a RAMEE system using two identical LAMEEs is0.0<Q_(sur)/Q_(exch)<0.05.

Since the liquid is under a pressure greater than the adjacent channelair pressure, it causes the flexible semi-permeable membrane and itssupport structure in the air channel on either side of each liquid flowchannel to deflect or deform elastically. As previously noted, theliquid flow should be directed through each channel so that it minimizesflow mal-distributions (i.e. Ra<Ra_(c) for laminar flow and, when flowrates are higher, Re>Re_(c) for turbulent flow). The design andoperational conditions imply that the liquid flow direction will be suchthat the liquid flow will be from a bottom inlet to the top outlet forthe supply LAMEE exchanger and from the top inlet to the bottom outletfor the exhaust LAMEE exchanger for the standard summer test conditions.The flow directions through each LAMEE will be reversed for the winterstandard test conditions. That is, a liquid flow direction controllerwill be used so that the inlet direction will be bottom or top of eachLAMEE exchanger depending on the value of the Rayleigh number for eachexchanger and the angles of the flow channels with respect to theacceleration direction of gravity as defined in Table 1 for factors G9and G10. With these controlled liquid flow directions and a smallperformance enhancing tilt angle for the LAMEE, the problems of flowmal-distribution will have been reduced to a minimum for the geometricconfigurations of the flow channels and the channel Reynolds number.

The Reynolds number for the liquid flow through the liquid flow channelswill typically be very low (i.e. 0.1<Re_(dh,liq)<100). Under thesecircumstances, the liquid flow may be laminar for the lowest Reynoldsnumbers in the range but, for some specially designed internalgeometries the flow will become complex-laminar-turbulent or turbulentas the Reynolds number is increased from the low to the high end of thisReynolds number range. Therefore the liquid channel flow, which mayexhibit laminar flow mass flux channeling or fingering of the liquid forunfavorable Rayleigh numbers at the low Reynolds numbers in the aboverange, will, due to turbulent mixing, locally self adjust at higherReynolds number so that mal-distribution effects are much smaller.

This is also a problem for laminar flows and heat and mass transfercoefficients. The liquid channel screen insures a minimum spacing forthe channel width and enhances the transition to turbulent flow forlarge liquid flow rates. The air and liquid flow channel screen arearatios (factor G6) is yet another predetermined embodiment because theratios are directly related to turbulence enhancement and blockagefraction of the membrane for water vapor transfer on the air side of themembrane. The air channel spacer support structure ratio (factor G7) isanother geometric embodiment that assists the transition to turbulentflow and partly determines the geometry of the flow channel through itsstructural supports. Factor G8 defines the best liquid flow directionwith respect to gravity through each LAMEE exchanger which may becontrolled to avoid liquid flow mal-distribution and factors G9 and G10define LAMME angles with respect to gravitational acceleration to gethigh performance factors for the RAMEE system and all its LAMEEs.

The new ratio of standard deviation for each liquid flow stream-tubehydraulic diameter in each liquid flow channel divided by the mean valuecan be used to analyze the decrease in expected effectiveness of eachLAMEE and the passive RAMEE system in which it is used or tested. Forexample, if the flow tube standard deviation ratio is 0.05 (i.e. 5%) forthe typical liquid flow channel in each identical LAMEE in the RAMEEsystem, then the decrease in total system effectiveness will be about 4%for turbulent flows but the loss of effectiveness may be much higher forlaminar liquid flows where the flow field is unstable due to buoyancyeffects.

Another embodiment is provided for the flow channels in each LAMEE whichinvolves flow field characterization through the Reynolds number and theflow stability factor, Rayleigh number. The Rayleigh number can beselected to be most favorable by arranging the temperature gradients ineach LAMEE to be such that the fluid density always increases in thedownward direction of gravitational acceleration. This implies that theflow channels in a LAMEE should be aligned so that their normal areavector is horizontal and the length vector of the flow channel is tiltedwith a large enough angle to cause a favorable and significant densitygradient for uniform flows in each channel and among all the channels.Channel flows in long thin channels with small or negligible entrancelengths for the flows are well known to be one of: (a) fully developedlaminar flow at low Reynolds number, (b) fully developed turbulent flowat high Reynolds number, or (c) transition turbulent flows atintermediate Reynolds numbers between the two low and high transitionReynolds numbers. The flow transition Reynolds number that causes theflow to transfer from laminar to transition turbulence tends to be fixedfor any given channel where the Rayleigh number indicates no buoyancyinduced mal-distributions, but very small changes to the surfaces insideeach channel can cause large changes to the transition Reynolds number.That is, the flow in a channel can become turbulent when small increasedsurface roughness or flow separations within the channel flow changesare introduced at some low Reynolds numbers compared to laminar flow inthe same channels with no roughness additions.

Turbulent flows in channels with flow at a particular Reynolds numberwill have enhanced heat and mass transfer rates compared with those withlaminar flows. Accordingly, the internal surface roughness may beenhanced for channel flows that would have been laminar for smoothinternal surfaces but turbulent for the same channel with rough surfacesor flow separation causing surfaces at the same Reynolds number (i.e.operating close to the flow transition Reynolds number between laminarand transition turbulence so as to cause the laminar flow to becometurbulent). The heat or mass transfer enhancement is a factor for theair flow channels where the relatively high laminar flow characteristicconvection resistance dominates the total resistance and the design needfor the LAMEE energy exchange total area and LAMEE total volume andgeometry. Air channel support structures must be chosen and positionedto provide the desired membrane channel width and concurrently induce aturbulent flow transition from laminar to turbulent flow, but not causean excessive increase air pressure drop for the flow channel. The ratiosfor the same channel flow Reynolds number are empirically selected forenhanced heat and mass transfer coefficients compared to laminar flowheat and mass transfer coefficients, which may be large, while theratios for increased friction coefficients compared to laminar flowfriction coefficients may be smaller (i.e. there is a net heat and masstransfer benefit for the turbulence enhancement relative to the air flowpressure drop increase).

On the liquid flow side of the membrane, turbulent mixing within theflow channel may be a factor if there is a tendency toward laminar flowbuoyancy induced mass flux fingering at high Rayleigh numbers and verylow Reynolds numbers result in non-uniform exposure of the bulk flow tothe molecular diffusion transfer process in the liquid. In oneembodiment, for the factor P1, turbulence enhancement of the air andliquid flows through the LAMEE energy exchange channels is used toenhance turbulent transition and liquid flow directions are chosen foreach LAMEE operating condition to decrease buoyancy inducedinstabilities in the liquid flow channels. For a given flow channelgeometry, which is characterized by the hydraulic diameter and surfaceroughness, the Reynolds number is the only operating factor thatdetermines whether the flow is laminar or turbulent. The performanceeffectiveness and RER of the passive RAMEE and its LAMEEs will beenhanced with some turbulent mixing.

In other embodiments, an energy exchanger is provided. The exchangerincludes a housing for the air and liquid desiccant channels eachseparated by a semi-permeable membrane. A plurality of panels formingdesiccant channels and air channels extend through the housing. The airchannels are configured to direct an air stream through the housing. Theplurality of panels are spaced apart based on predetermined air todesiccant channel rates that define an air channel width or spacing anda desiccant channel width or spacing. A desiccant inlet header isprovided in flow communication with all the desiccant channels. Adesiccant outlet is provided in flow communication with the desiccantchannels. The desiccant channels are configured to channel desiccantfrom the desiccant inlet to the desiccant outlet in at least one of acounter-flow or cross-flow direction with respect to the direction ofthe air stream to facilitate heat and water vapor transfer between thedesiccant in the desiccant channels and the air stream in the airchannels. For a predetermined test condition of the passive RAMEEsystem, a predetermined equal mass flow rate of supply and exhaust airpass through each identical LAMEE. By so doing, the number of transferunits for heat transfer (NTU) in each LAMEE is predetermined (factorP2). When the pumping rate of liquid desiccant is chosen, the heatcapacity rate ratio (i.e. the mass flow rate times the specific heat ofdesiccant liquid flow divided by the mass flow rate of air) through eachLAMEE, Cr*, is predetermined (factor P3). There may be a trade-off forthe selection of Cr* because increasing the liquid flow rate may enhanceturbulence in the liquid flow channels and will increase Cr*, which canhave positive and negative effects on the effectiveness. Accordingly,the value of Cr* should be selected so that the effectiveness of theLAMEE is a maximum when the highest performance is required.

Other embodiments for energy exchangers are provided. The exchangerincludes a housing containing the air and liquid flow channels eachseparated by a semi-permeable membrane. A plurality of panels formingdesiccant channels and air channels extend through the housing. The airchannels are configured to direct an air stream through the housing. Adesiccant inlet header is provided in flow communication with all thedesiccant channels. A desiccant outlet is provided in flow communicationwith the desiccant channels. The desiccant channels are configured tochannel desiccant from the desiccant inlet to the desiccant outlet in atleast one of a counter-flow or cross-flow w direction with respect tothe direction of the air stream. A desiccant membrane extends througheach panel to facilitate heat and water vapor transfer between thedesiccant liquid in the desiccant channels and the air stream in the airchannels. The semi-permeable membrane possesses a resistance to watervapor diffusion which, relative to the typical convection water vaportransport resistance in the air channels, lies within a specified rangegiven by factor P4.

The static air pressure drop as it passes from air inlet to outlet ineach LAMEE in a RAMEE system is the same for each air channel. The rangeof acceptable air pressure drops for a LAMEE so that the passive RAMEEsystem will have a high RER value in the set Pf is presented usingfactor P5.

As discussed previously, inducing turbulence for otherwise laminarflows, for both the air-flow and liquid-flow channels, can enhance theheat and mass transfer coefficients more than the flow frictioncoefficients. Factor P6 defines the circumstance when there will be anet benefit for inducing turbulence in either the air or liquidchannels.

In another embodiment for a passive RAMEE system, the exchanger includesa housing. A plurality of panels forming desiccant channels extendthrough the housing. Each of the plurality of panels has asemi-permeable membrane separating the air flow channels from the liquidflow channels. Air channels are formed between the desiccant liquidchannels. The air channels are configured to direct an air streamthrough the housing. A desiccant inlet is provided in flow communicationwith the desiccant channels. A desiccant outlet is provided in flowcommunication with the desiccant channels. The desiccant channels areconfigured to channel desiccant from the desiccant inlet to thedesiccant outlet so that the semi-permeable membranes facilitate heatand water vapor exchange between the liquid desiccant and the adjacentair streams in a LAMEE. During a standard test with two identical LAMEEsin a passive RAMEE test loop, heat will be transferred between theLAMEEs and their surroundings. The relative magnitude of the heattransfer between the surroundings and each LAMEE is designed to be asmall fraction of the heat rate between the air flows passing throughthe LAMEEs (factor P12).

FIG. 1 illustrates a passive run-around membrane energy exchange (RAMEE)system 100 formed in accordance with an embodiment. The RAMEE system 100is configured to partly or fully condition air supplied to a structure101. The RAMEE system 100 includes an inlet 102 for a pre-conditionedair flow path 104. The pre-conditioned air flow path 104 may includeoutside air, air from a building adjacent to the enclosed structure 101,or air from a room within the enclosed structure 101. Airflow in thepre-conditioned air flow path 104 is moved through the pre-conditionedair flow path 104 by a fan 106. The illustrated embodiment includes onefan 106 located upstream of the LAMEE 108. Optionally, thepre-conditioned air flow path 104 may be moved by a down-stream fan andby multiple fans or a fan array or before and after each LAMEE in thesystem. The fan 106 directs the pre-conditioned air flow through path104 to a supply liquid-to-air membrane energy exchanger (LAMEE) 108. Thesupply LAMEE 108 conditions the pre-conditioned air flow in path 104 togenerate a change in air temperature and humidity (i.e. topre-conditioned the air partly or fully) toward that which is requiredfor a supply air flow condition to be discharged into the enclosed space101. During a winter mode operation, the supply LAMEE 108 may conditionthe pre-conditioned air flow path 104 by adding heat and moisture to thepre-conditioned air in flow path 104. In a summer mode operation, thesupply LAMEE 108 may condition the pre-conditioned air flow path 104 byremoving heat and moisture from the pre-conditioned air in flow path104. The pre-conditioned air 110 is channeled to a HVAC system 112 ofthe enclosed structure 101. The HVAC system 112 may further conditionthe pre-conditioned air 110 to generate the desired temperature andhumidity for the supply air at 114 that is supplied to the enclosedstructure 101.

Return air 116 is channeled out of the enclosed structure 101. A massflow rate portion 118 of the return air 116 is returned to the HVACsystem 112. Another mass flow rate portion 119 of the return air 116 ischanneled to a return LAMEE 120. The portions 118 and 119 may beseparated with a damper 121 or the like. For example, 80% of the returnair 116 may be channeled to the HVAC system 112 and 20% of the returnair 116 may be channeled to the return air regeneration LAMEE 120 in theRAMEE loop. The return air LAMEE 120 exchanges energy between theportion 118 of the return air 116 and the preconditioned air 110 in thesupply air LAMEE 108. During a winter mode, the return air LAMEE 120collects heat and moisture from the portion 118 of the return air 116.During a summer mode, the return air LAMEE 120 discharges heat andmoisture into the regeneration air flow 119. The return air LAMEE 120generates exhaust air 122. The exhaust air 122 is discharged from thestructure through an outlet 124. A fan 126 is provided to move theexhaust air 122 from the return air LAMEE 120. The RAMEE system 100 mayincludes multiple fans 126 or one or more fan arrays located eitherup-stream or down-stream (as in FIG. 1) of the exhaust air LAMEE 120.

A desiccant fluid 127 flows between the supply air LAMEE 108 and thereturn air LAMEE 120. The desiccant fluid 127 transfers the heat andmoisture between the supply air LAMEE 108 and the return air LAMEE 120.The RAMEE system 100 includes desiccant storage tanks 128 in fluidcommunication between the supply air LAMEE 108 and the return air LAMEE120. The storage tanks 128 store the desiccant fluid 127 as it ischanneled between the supply air LAMEE 108 and the return air LAMEE 120.Optionally, the RAMEE system 100 may not include both storage tanks 128or may have more than two storage tanks. Pumps 130 are provided to movethe desiccant fluid 127 from the storage tanks 128 to one of the supplyLAMEE 108 or the return LAMEE 120. The illustrated embodiment includestwo pumps 130. Optionally, the RAMEE system 100 may be configured withas few as one pump 130 or more than two pumps 130. The desiccant fluid127 flows between the supply air LAMEE 108 and the return air LAMEE 120to transfer heat and moisture between the conditioned air 110 and theportion 118 of the return air 116.

The embodiments described herein utilize a set of predeterminedgeometric design factors (G1-G10) and physical property and operatingparameters (P1-P12) for the supply and exhaust air LAMEEs 108 and 120and the RAMEE system 100 and maintain predetermined ranges for eachparameter for LAMEEs 108 and 120 and for the RAMEE system 100, asillustrated in Table 1. As a set, the design and operating parametersenable the systems to meet selected performance factors. The set ofpredetermined geometric design and physical property and operatingparameters is comprised of a subset of geometric design length ratiosand a subset of physical property and operating parameters eachcomprised of physical property or operating condition ratios that mayinclude some geometric lengths as well as other physical properties insome cases. The defined geometric design and physical ratios representdimensionless ratios or factors that do not require specific lengthscales or property units except with respect to another defined lengthor parameter with the same units in the same ratio (i.e. each of them isdimensionless). The geometric design and physical parameters arediscussed herein in connection with various embodiments.

The performance factors for a RAMEE system 100 employing supply andexhaust air counter-flow or cross-flow LAMEEs 108 and 120, in accordancewith the embodiments, may be determined using ASHRAE Std. 84-2008 usinga defined set of steady-state test conditions defined in AHRI Std.1060-2005. In one embodiment, a thermal insulation surrounding thepanels is such that a heat exchange rate between the panels is less than5% of a heat rate between supply and exhaust air flow streams duringstandard summer or winter testing with AHRI 1060 air inlet operatingconditions. The operating conditions for the RAMEE system 100 during atest with balanced air flows and with the system at or very nearsteady-state will be determined by specifying: Cr*, NTU, NTU_(m) and therelative flow direction and geometry of each LAMEE (where each of thedimensionless terms have been defined previously or will be definedherein). The deduction of the effectiveness of performance of a singleLAMEE 108 from the steady-state or quasi-steady-state RAMEE system 100test data, which includes two similar LAMEEs, 108 and 120, may bededuced from steady-state energy and mass balance equations. That is,both the overall run-around system effectiveness, E₀, and the individualexchanger effectiveness, E, in the run-around loop depends on Cr*, NTUand NTU_(m) at or near steady state so the relationship for E can bereadily determined once E₀ is measured. For the simple example of arun-around heat exchanger system with equal supply and exhaust air flowrates using two identical counter flow heat exchangers, it can be shownthat Cr=1.0 at the maximum heat rate and system overall effectiveness,E₀, and the individual supply or exhaust exchanger effectiveness isgiven by:E=2E ₀/(1+E ₀) which will have a relative uncertainty of U(E)/E=2U(E₀)/[E ₀(1+E ₀)²] where both E and E ₀ are less than 1.0 for heatexchangers{e.g. when E ₀=⅔ (or 67%)(calculated from the measured data) and U(E₀)/E ₀=0.05 (also determined from data) then E=0.80+/−0.04 (or 80+/−4%)}

In one embodiment, the flow panel aspect ratio is defined by the heightof the energy exchange area of each flow panel divided by the length ofthe same exchange area in the LAMEE. In another embodiment, the entrancelength to total panel length ratio is defined for LAMEEs that are eitherprimarily counter-flow or cross-flow exchangers. In another embodiment,the ratio of the flow channel standard deviation of average panelchannel hydraulic diameters (widths) for each fluid with respect toaverage flow hydraulic diameter (width) for each fluid for the LAMEE islimited to reduce mal-distribution of fluid flows among the channels. Inanother embodiment, the ratio of the stream-tube standard deviation inhydraulic diameter to mean stream-tube hydraulic diameter is limited toreduce flow mal-distributions within a typical flow channel. The liquiddesiccant to air capacity rate ratio also implies a particular mass flowrate ratio. Therefore, for a predetermined volume or mass flow rate ofair flowing through the air channels of a LAMEE and a particular volumeor mass flow rate of liquid desiccant may be required to flow throughthe adjacent liquid desiccant channels.

In another embodiment, turbulent flow conditions are induced in the airand liquid flow channels of the LAMEE by selecting a distribution andgeometric shape for the air and liquid flow channel spacers in theLAMEE. The turbulence can be used to enhance the heat and mass transferconvection coefficients in the air flow channels which can be used toincrease the effectiveness and/or decrease the LAMEE size. In otherembodiments for the liquid flow channels, turbulence in the liquid flowchannels is facilitated to enhance the bulk mean flow distribution (andeliminate laminar flow fingering and mal-distributions) and increase theconvective heat and moisture transfer coefficients (i.e. decreasemal-distributions in the liquid flows) because the physical effectincreases the effectiveness of a given LAMEE and its RAMEE system andcan be used to decrease the physical size of each LAMEE.

In another embodiment, the elastic tensile limit for the semi-permeablemembrane is selected to partly limit the deflection of thesemi-permeable membrane with respect to its structural support screen inthe LAMEE.

In another embodiment, the membrane and membrane frame liquid flowpenetration resistance ranges are selected to eliminate any flow of theliquid desiccant through the semi-permeable membrane and its edge sealframe for each panel pair of channels in the LAMEE.

In another embodiment, the air mass flow ratio of the two air streamsinlet to the two identical LAMEEs in the RAMEE system is selected tomeet a predetermined exposure of the air stream to the semi-permeablemembranes.

In another embodiment, the air pressure drop ratio for a selected massflow rate of air is selected to ensure a high RER performance factor fora RAMEE system.

In another embodiment, the salt solution concentration ranges are usedto limit the time fraction when there may be a risk of crystallizationfor a climatic region for particular application and reduce thelife-cycle costs for an application.

In another embodiment, the heat exchange with the surroundings is byusing appropriate energy exchange cavity insulation reduced to a smallfraction of the heat rate for the RAMEE system under a standard test.

FIG. 2 illustrates a LAMEE 300 formed in accordance with an embodiment.The LAMEE 300 may be used as the supply air LAMEE 108 and/or the returnor exhaust air LAMEE 120 (shown in FIG. 1). The LAMEE 300 includes ahousing 302 having a body 304. The body 304 includes an air inlet end306 and an air outlet end 308. A top 310 extends between the air inletend 306 and the air outlet end 308. A stepped-down top 312 is positionedat the air inlet end 306. The stepped-down top 312 is stepped a distance314 from the top 310. A bottom 316 extends between the air inlet end 306and the air outlet end 308. A stepped-up bottom 318 is positioned at theair outlet end 308. The stepped-up bottom 318 is stepped a distance 320from the bottom 316. In alternative designs the stepped-up 318 orstepped-down 312 sections may have different sizes of steps or no stepat all.

An air inlet 322 is positioned at the air inlet end 306. An air outlet324 is positioned at the air outlet end 308. Sides 326 extend betweenthe air inlet 322 and the air outlet 324. Each panel in the LAMEE 300has a semi-permeable membrane length 364, as shown in FIG. 3 a. Alsoshown in FIG. 3 a, each panel in the LAMEE 300 has a semi-permeablemembrane height 362 defining an energy exchange area extends a height(H) between a top and a bottom defined by the top and bottom of thesemi-permeable membrane. The energy exchange area extends a length (L)between a front and a back that is defined by the front and the back ofthe semi-permeable membrane. An exchanger aspect ratio (AR) is definedby a height (H) 362 of each semi-permeable membrane energy exchange areadivided by a length (L) 364 of the energy exchange area. The exchangeraspect ratio (AR) represents the physical design factor G2 (shown inTable 1) and is at least one factor for partly achieving a predeterminedperformance of the LAMEE 300. The aspect ratio (AR) is a dimensionlessratio. The aspect ratio (AR) is determined using the equation AR=H/L. Inan exemplary embodiment for a counter/cross flow LAMEE, factor G2, theaspect ratio (AR), is within a range of 0.1<AR<3.0. In one embodiment,the exchanger aspect ration is within a range of 0.5 to 2. The exchangeraspect ratio is selected to provide at least one of a predeterminedmembrane area, a predetermined length, or a predetermined duration ofexposure of the air stream to the desiccant.

An energy exchange cavity 330 extends through the housing of the LAMEE.The energy exchange cavity 330 extends from the air inlet end 306 to theair outlet end 308. An air stream 332 is received in the air inlet 322and flows through the energy exchange cavity 330. The air stream 332 isdischarged from the energy exchange cavity 330 at the air outlet 324.The energy exchange cavity 330 includes a plurality of panels 334. Eachliquid flow panel forms a liquid desiccant channel 376 that is confinedby the semi-permeable membranes 378 on either side and is configured tocarry desiccant 341 therethrough. The semi-permeable membranes 378 arearranged in parallel to form air channels 336 with an average flowchannel width (d_(w,air)) of 337 and liquid desiccant channels 376 withan average flow channel width (d_(w,liq)) of 377. In one embodiment, thesemi-permeable membranes 378 are spaced to form uniform air channels 336and liquid desiccant channels 376 with d_(w,air) and d_(w,liq) impliedby what is practical to reduce statistical variations for each asillustrated in factor G4 of Table 1. The air stream 332 travels throughthe air channels 336 between the semi-permeable membranes 378. Thedesiccant 341 in each desiccant channel 376 exchanges heat and moisturewith the air stream 332 in the air channels 336 through thesemi-permeable membranes 378.

A desiccant inlet reservoir 338 is positioned on the stepped-up bottom318. The desiccant inlet reservoir 338 may have a height 340 equal tothe distance 320 between the bottom 316 and the stepped-up bottom 318.Alternatively, the liquid desiccant inlet reservoir 338 may have anyheight 340 that meets a predetermined performance of the LAMEE 300. Thedesiccant inlet reservoir 338 extends a length 339 of the LAMEE body304. The desiccant inlet reservoir 338 extends a length 339 that isconfigured to meet a predetermined performance of the LAMEE 300. In oneembodiment the desiccant inlet reservoir 338 extends no more than onefourth of the length 327 of the LAMEE body 304. Alternatively, thedesiccant inlet reservoir 338 may extend along one fifth of the length327 of the LAMEE body 304.

The liquid desiccant inlet reservoir 338 is configured to receivedesiccant 341 from a storage tank 128 (shown in FIG. 1). The desiccantinlet reservoir 338 includes an inlet 342 in flow communication with thestorage tank 128. The desiccant 341 is received through the inlet 342.The desiccant inlet reservoir 338 includes an outlet 344 that is influid communication with the desiccant channels 376 in the energyexchange cavity 330. The liquid desiccant 341 flows through the outlet344 into the desiccant channels 376. The desiccant 341 flows along thepanels 334 through desiccant channel 376 to a desiccant outlet reservoir346.

The desiccant outlet reservoir 346 is positioned on the stepped-down top312 of the LAMEE housing 302. Alternatively, the desiccant outletreservoir 346 may be positioned at any location along the top 312 of theLAMEE housing 302 or alternatively on the side of the reservoir with aflow path connected to all the panels. The desiccant outlet reservoir346 has a height 348 that may be equal to the distance 314 between thetop 310 and the stepped-down top 312. The desiccant outlet reservoir 346extends along the top 312 of the LAMEE housing 302 for a length 350. Inone embodiment of a counter/cross flow exchanger, the desiccant outletreservoir 346 extends a length 350 that is no more than one fourth thelength 327 of the flow panel exchange area length 302. In anotherembodiment of a counter/cross flow LAMEE the desiccant outlet reservoir346 extends a length 350 that is one fifth the length 327 of the panelexchange area length 302 (i.e. factor G3).

The desiccant outlet reservoir 346 is configured to receive desiccant341 from the desiccant channels 376 in the energy exchange cavity 330.The desiccant outlet reservoir 346 includes an inlet 352 in flowcommunication with the desiccant channels 376. The desiccant 341 isreceived from the desiccant channels 376 through the inlet 352. Thedesiccant outlet reservoir 346 includes an outlet 354 that is in fluidcommunication with a storage tank 128. The desiccant 341 flows throughthe outlet 354 to the storage tank 128 where the desiccant 341 is storedfor use in another LAMEE 300. In an alternative embodiment, thedesiccant outlet reservoir 346 may be positioned along the bottom 318 ofthe LAMEE housing 302 and the desiccant inlet reservoir 338 may bepositioned along the top 310 of the LAMEE housing 302.

In the illustrated embodiment, the LAMEE 300 includes one liquiddesiccant outlet reservoir 346 and one liquid desiccant inlet reservoir338. Alternatively, the LAMEE 300 may include liquid desiccant outletreservoirs 346 and liquid desiccant inlet reservoirs 338 on the top andbottom of each of each end of a LAMEE 300. A liquid flow controller maydirect the liquid flow to either the top or bottom depending on thevalue of Ra for factor P1 in the independent factor set If in Table 1.

During testing of the RAMEE system 100 using ASHRAE Std. 84-2008 and thesteady-state test conditions defined in AHRI Std. 1060-2005, wherein theRAMEE system 100 has balanced air flows and is at or very nearsteady-state, an exchanger thermal capacity ratio Cr* (operationalindependent factor P3 as illustrated in Table 1) is defined. Cr* is adimensionless ratio representing the mass flow rate of the liquiddesiccant times the heat capacity of the liquid desiccant divided by themass flow rate of the air times the heat capacity of the air. Cr* ismeasured by measuring the flow rates of the air and liquid desiccant andusing known heat capacities of the liquid desiccant and the air. In oneembodiment, Cr* falls within a range during RAMEE testing that isbetween 1.0<Cr*<10.0. In one example for a run-around heat exchangersystem having equal supply and exhaust air flow rates and using twoidentical counter flow heat exchangers, Cr* may equal 1.0 at a maximumheat rate and overall effectiveness, E₀.

During RAMEE testing, the exchanger number of transfer units (NTU) forheat transfer (operational independent factor P2 as illustrated inTable 1) may also be defined. In general, the effectiveness of a heatexchanger increases directly with the value of NTU. A heat capacity ratefor the air stream 332 and the desiccant 341 is used to determine themaximum feasible heat transfer between the air stream 332 and thedesiccant 341. The effectiveness of the RAMEE system for heat transferbetween the supply air flow and the exhaust air flow is determined bymeasuring the two mass flow rates of air and the temperature increase ofthe air flowing through the supply air exchanger and the temperaturedifference between the inlet air to the supply and exhaust airexchangers. In one embodiment, NTU is within a range 1<NTU<15. Having anNTU within this range may provide a predetermined performance of theRAMEE system. In one embodiment, the range of NTU may functionconcurrently with other performance factors defined herein to achievethe predetermined performance of the LAMEE 300 and the RAMEE system 100.

During RAMEE 100 testing, an air flow pressure drop ratio (operationaldesign factor P4 as illustrated in Table 1) may also be defined for theLAMEEs 300. The air flow pressure drop ratio is calculated using theratio p_(h)A_(c)/V_(c), wherein p_(h) is the air flow pressure head dropacross the LAMEE 300, A_(c) is the energy exchange area of one air flowchannel in LAMEE 300, and V_(c) is the volume of each air channel. Theair flow pressure drop ratio is used to define a pressure drop in theair stream 332 between the air inlet 322 and the air outlet 324 of theLAMEE 300. In one embodiment, the air flow pressure drop ratio is with arange of 10³ to 10⁴ to achieve a predetermined RER performance factorfor the RAMEE system 100.

FIG. 3 a illustrates the LAMEE 300 having a cutout along the line 3-3shown in FIG. 2. The top 310 and the bottom 318 of the LAMEE housing 302include insulation 360 joined thereto. The sides 326 of the LAMEEhousing 302 also include insulation 360. Except for the air inlet andoutlet areas, the insulation 360 extends around the energy exchangecavity 330. The insulation 360 limits an amount of heat that may beexchanged between the air and liquid desiccant flowing through theenergy exchange cavity and the surroundings as the air and liquiddesiccant flow through the channels in the energy exchange cavitycompared to the heat rate for the air for the supply and exhaust airflows (i.e. factor P12). The insulation 360 may include foam insulation,fiber insulation, gel insulation, or the like. The insulation 360 isselected to at least partially meet a predetermined performance of theLAMEE 300.

The energy exchange cavity 330 has a height 362, a length 364, and awidth 366. The height 362 is defined between the top and bottom of theenergy exchange cavity 330. The width 366 is defined between theinsulation side walls of the energy exchange cavity 330. The length 364is defined between the air inlet 322 and the air outlet 324 of theenergy exchange cavity 330. Each energy exchange panel 334 extends theheight 362 and length 364 of the energy exchange cavity 330. The panels334 are spaced along the width 366 of the energy exchange cavity 330.

For the counter/cross flow LAMEE, the liquid desiccant flow inlet 334 ofthe desiccant inlet reservoir 338 is in flow communication with theenergy exchange cavity 330 at the air outlet end 308 of the LAMEE 300.The liquid desiccant outlet 352 of the desiccant outlet reservoir 346 isin flow communication with the energy exchange cavity 330 at the airinlet end 306 of the LAMEE 300. The desiccant inlet reservoir 338 andthe desiccant outlet reservoir 346 are in fluid communication with theliquid channel 376. The panels 334 define a non-linear liquid desiccantflow path 368 between the desiccant inlet reservoir 338 and thedesiccant outlet reservoir 346. The flow path 368 illustrates oneembodiment of a counter/cross flow path with respect to the direction ofthe air stream 332. In one embodiment, a desiccant flow directionthrough the desiccant channels 376 is controlled so that lower densitydesiccant flows separately from higher density desiccant.

FIG. 3 b illustrates a front view of the panels 334. The panels 334 arespaced to form air channels 336 and the liquid desiccant channels 376there-between separated by semi-permeable membranes 378. The airchannels 336 alternate with the liquid desiccant channels 376. Exceptfor the two side panels of the energy exchange cavity, each air channel336 is positioned between adjacent liquid desiccant channels 376. Theliquid desiccant channels 376 are positioned between adjacent airchannels 336. The air channels 336 have an average channel width 337defined between adjacent panels 334. The liquid desiccant channels 376have an average channel width 377 defined between adjacent panels 334.The width 337 of the air channels 336 and the width 377 of the liquiddesiccant channels 376 are nearly constant over the area of each paneland for the set of panels in the LAMEE energy exchange cavity with theexception of independent geometric design factors G4 and G5 asillustrated in Table 1. In one embodiment, the standard deviation of theaverage channel hydraulic diameter (directly related to the width 337 ofthe air channels 336 or average channel width 377 of the liquiddesiccant channels 376) divided by the corresponding mean averagechannel hydraulic diameter for each fluid is an independent geometricdesign factor (physical design factor G4 as illustrated in Table 1)restricted for each type of fluid channel to at least partly achieve thepredetermined set of performance factors Pf of the RAMEE system with itsLAMEEs 300. In another embodiment, the statistical variations in thestream-tube hydraulic diameters will be such that the standard deviationof the flow tubes hydraulic diameters for a typical type of fluidchannel in a LAMEE divided by the mean stream-tube hydraulic diameterfor the typical flow channel of a fluid will be restricted as specifiedby factor G5 in Table 1.

FIG. 4 illustrates a panel 334 to contain the desiccant liquid flow forone channel formed in accordance with an embodiment. The panel 334includes support structures including a top support 370, a bottomsupport 372 that is opposite the top support 370, and a pair of oppositeside supports 374 extending between the top support 370 and the bottomsupport 372. The supports 370, 372, and 374 retain the membranes 392 anda liquid desiccant inlet diffuser 396 and outlet diffuser 400. The panel334 includes a top 381 and a bottom 383. The panel 334 has an overallheight 382 defined between the top 381 and the bottom 383. The energyexchange membrane 392 includes a top 385 and a bottom 387. The membrane392 has an overall height 384 defined between the top 385 and the bottom387. The height 384 of the membrane 392 is less than the height 382 ofthe panel 334. The panel 334 has a front end 389 and a back end 391. Thepanel 334 has an overall length 386 defined between the front end 389and the back end 391. The membrane 392 includes a front end 393 and aback end 395 corresponding to the air inlet and outlet for the adjacentair flow channels respectively. The membrane 392 has an overall length388 defined between the front end 393 and the back end 395. The length388 of the membrane 392 is less than the length 386 of the panel 334.Ratios of the heights 382 and 384 to the lengths 386 and 388,respectively, may be configured based at least partly on a predeterminedperformance of the LAMEE 300. In one embodiment for a counter/cross-flowpanel, the height 384 of the membrane 392 is within a range of 0.1 to3.0 times the length 388 of the membrane 392 (i.e. factor G2).

The panel 334 has a desiccant inlet end 378 and a desiccant outlet end380. A desiccant flow path 368 shows a typical bulk mean streamline forflow from the liquid desiccant inlet 396 to the desiccant outlet 400 ina non-linear flow path that is primarily opposite to the direction ofthe air stream 332. The desiccant inlet end 378 includes an inlet 390that extends through the bottom support 372 and between adjacent panels334. The inlet 390 has a length 396. A ratio of the length 396 of theinlet 390 to the length 388 of the panel 334 is selected based on apredetermined performance of the LAMEE. The desiccant outlet end 380includes an outlet 398 that extends through the top support 370 andbetween adjacent panels 334. The outlet 398 has a length 400 which isequal to the inlet length 396. A ratio of the length 400 of the outlet398 to the length 388 of the panel 334 is selected based at least partlyon a predetermined performance of the LAMEE 300. The desiccant flow path368 flows from the inlet 390 to the outlet 398.

The liquid desiccant flow path-line 368 is the same as one possiblebulk-mean streamline which is necessarily curved, especially near theliquid ingest and egress regions of the channel, through acounter/cross-flow panel of a LAMEE. The curved streamline is contrastedwith the essentially straight bulk-mean air streamline 332 in the airchannels 336. The bulk-mean liquid desiccant flow path direction orvelocity is mostly upstream of that for the adjacent channel bulk-meanair stream 332. An inlet flow ingest region cross segment 402 of theliquid desiccant bulk-mean streamline 368 is formed as the desiccantenters the desiccant channel 376 from the inlet 390. Liquid desiccant341 flowing from the inlet 390 into the desiccant channel 376 flowsupward through the inlet cross segment 402. Liquid desiccant 341 in theinlet cross segment 402 flows partly in a cross flow direction to thatfor the adjacent air flow channel streamline 332.

Since the liquid desiccant 341 is channeled from the inlet 390, thedesiccant 341 fills the channel 376 and flows through a primarily anair/liquid counter flow segment 404 of the liquid desiccant bulk-meanstreamline 368. The liquid/air counter flow segment 404 extendsapproximately a length 406 through the liquid desiccant flow channel376. The length 406 is based partly on a predetermined performance ofthe LAMEE 300. The liquid/air counter flow segment 404 is essentiallyparallel to direction of the air stream 332 in the air channels 336. Theliquid/air counter flow segment 404 has the liquid flow opposite to thedirection of the adjacent air flow 332. The counter flow arrangement atleast partly provides a predetermined heat and moisture exchangeeffectiveness between the liquid desiccant 341 in the desiccant channel376 and the air stream 332 in the air channels 336.

The liquid desiccant 341 in the counter segment 404 flows into acounter/cross-flow liquid flow egress region 408 of the liquid desiccantflow path 368. The liquid desiccant 341 in the outlet counter/cross flowregion segment 408 flows with curved bulk mean streamlines from thecounter segment 404 to the outlet 398. The liquid desiccant 341 in theoutlet counter/cross flow region 408 flows at least partly in a crossflow direction that is perpendicular to the direction of the air stream332 in the air channels 336.

The counter/cross-flow arrangement of the liquid desiccant bulk-meanstreamline flow path 368 provides a liquid desiccant nearly counter flowwith respect to the air stream 332. The counter flow arrangementimproves the effectiveness of the LAMEE 300 compared to a unit withequal mass flow rates, inlet properties and exchanger energy exchangearea. The counter/cross flow arrangement does not require large headersthat increase the space required for the LAMEE 300. The illustratedembodiment shows the desiccant flow path 368 flowing upward from theinlet 390 to the outlet 398. Optionally, the inlet 390 may be positionedat the top support 370, but at the same end of the panel 334 and theoutlet 398 may be positioned at the bottom support 372 but at the sameend of the panel 334. In such an embodiment, the desiccant flow path 368may flow downward from the inlet 390 to the outlet 398. The flowdirection option facilitates avoiding liquid channel flowmal-distributions caused by buoyancy induced instability in one of thetwo LAMEEs under typical summer and winter operating for a RAMEE system.

FIG. 5 a is an exploded view of the liquid desiccant flow panel 334. Thepanel 334 includes a liquid-desiccant flow guide andturbulence-enhancement screen diffuser 410 and a pair of semi-permeablemembranes 412. The liquid-desiccant screen diffuser 410 is retainedbetween the semi-permeable membranes 412. The semi-permeable membranes412 are bonded (by heat sealing or glue) to the membrane supportstructural elements 418 and 424. The membrane support screens 414 in theadjacent air flow channels 336 may also include air flow channelspacers. An air channel support screen may include a solid area that isa fraction of a total area of the air channel support screen.Additionally, a desiccant channel support screen may have a solid areathat is a fraction of a total area of the desiccant channel supportscreen. In one embodiment, a distance between air channel supportscreens in the flow direction of the air stream divided by a distancebetween air channel support screens normal to the flow direction of theair steam is within a range of 0.01 to 5.0. The air flow channels 336are formed between adjacent liquid-desiccant flow panels 334. Thedesiccant 341 is configured to have a bulk-mean flow parallel to thesemi-permeable membranes 412. The semi-permeable membranes 412 allowheat and moisture exchange between the flowing liquid-desiccant 341 inthe desiccant channels 376 and the flowing air stream 332 in the airchannels 336. The membrane 412 is semi-permeable and formed with a highdensity of micron-sized pores that allow water vapor to diffuse throughthe membrane 412 between the liquid desiccant 341 and the air stream332. The pores have a size that, due to air-liquid suffice tensionforces, prevents the liquid desiccant 341 from flowing through the poresof the membrane 412. The semi-permeable membrane material may beselected in part based on a required performance of the LAMEE 300.

FIG. 5 b is a more detailed view of the air flow channels comprising twomembranes, two structural support screens and many air flow channelstructural spacers. In an alternative design the spacers may be porousrigid tubes. The parameters for structurally supporting the flexiblemembranes for the air channel are specified by factor G7.

The membrane material may be selected, in part, based on a water vaporresistance diffusion (R_(m,wv)) divided by a convective water vaportransfer resistance into the adjacent air flow channels (R_(air,wv))(independent operational design factor P4 as illustrated in Table 1).The water vapor resistance (R_(m,wv)) is defined as the membrane'sresistance to water vapor diffusing through the membrane 412 between theair channel 336 and the liquid channel 376. The convective water vaportransfer resistance (R_(air,wv)) is defined as the membrane's ability toresist water vapor transfer between the bulk-mean flow of air inchannels 336 and the liquid channels 376 through the semi-permeablemembrane 412. The ratio of the water vapor diffusion resistance(R_(m,wv)) of the semi-permeable membrane 412 to the convective watervapor transfer resistance (R_(air, wv)) of the membrane 412 may have arange of 0.1<(R_(m,wv))/(R_(air,wv))<3.0 in factor P4. In oneembodiment, the ratio is selected to be as small as practical.

The semi-permeable membrane 412 may also be partly selected based on aliquid break through pressure of the membrane 412 (operational designfactor P7 as illustrated in Table 1). The liquid break through pressureis defined by a standard test as a liquid pressure within the LAMEE 300that is required for liquid desiccant 341 to flow through thesemi-permeable membrane 412. In one embodiment, factor P8, the membraneliquid break through pressure (p_(m,bt)), is selected to satisfy theinequality (p_(m,bt))/(rho*g*H)>20, where rho is the density of theliquid desiccant solution, g is the acceleration of gravity and H is theheight of the semi-permeable membrane in the energy exchange area of thesurface for each channel. A liquid break through pressure ratio isdefined by p_(m,bt)/(rho*g*H), wherein p_(m,bt) is the membrane liquidbreak-through pressure, g is gravity, and H is the height of themembrane panel energy exchange area. In one embodiment, the membraneliquid break through pressure may be greater than 20.

A channel edge seal liquid break-through pressure (p_(es,bt))(operational design factor P8 as illustrated in Table 1) defines apressure within the LAMEE 300 that is required for the desiccant 341 toflow through the edge seal of the membrane 412. The channel edge sealliquid break-through pressure (p_(es,bt)) is selected to satisfy theinequality p_(es,bt)/(rho*g*H)>20. When the operating pressure of theliquid flow channels is less than p_(m,bt) or p_(es,bt) no liquid leekswill occur through the membrane 412 or the edge seals. In oneembodiment, the edge seal liquid break through pressure may be greaterthan 20.

The membrane material may also be at least partly selected based on anelastic tensile yield limit (T_(m,yl)) (operational design factor P9 asillustrated in Table 1). The elastic tensile yield limit (T_(m,yl))defines the membrane's elastic deformation limits when subjected toliquid pressure from the desiccant 341 flowing through the desiccantchannel 376. In one embodiment, factor P9, the elastic tensile yieldlimit (T_(m,yl)) for the membrane 412, will lie in the range of0.02<(T_(m,yl))/(p_(l,op)*s_(ws))<1.5, where p_(l,op) is a typicaloperating pressure for the liquid in each LAMEE and s_(ws) is a wirespacing distance for the air-side screen 416 used to resist the liquidpressure for each desiccant channel 376. The operating pressure of theLAMEE is confined to a value that will not exceed the elasticdeformation limits for the membrane 412 for each desiccant channel 376.An elastic tensile yield limit ratio for the membrane is defined byT_(m,yl)/(p_(l,op)*s_(ws)), wherein T_(m,yl) is the tensile yield limitfor the membrane, p_(l,op) is a typical operating pressure for theliquid in each LAMEE, and s_(ws) is a wire spacing distance for a screenused to resist the liquid pressure for each liquid flow channel

Membrane air-side screen support structures 414 are positioned adjacentto the membranes 412. Each membrane 412 is positioned between anair-side membrane support structure 414 and the desiccant flow channelliquid-flow-guide screen diffuser 410. The membrane support structures414 retain the membranes 412 to limit the elastic deflections of themembranes 412. Deflection of the membranes 412 will occur due to liquidstatic pressure that is higher than that for the adjacent air channels332. The liquid desiccant will create pressure on the membranes 412 thatcauses the membranes 412 to bow and/or elastically deform. The mass flowmal-distribution on the adjacent liquid and air sides is tightlycontrolled for the design and quality control of the manufacturingprocess and operation of the RAMEE system and its LAMEEs.

In an example embodiment, the membrane air-side support structures 414are formed from a screen material. Optionally, the membrane supportstructures 414 may be formed from a permeable backing, plastic supportstructures, rods, metal screens, spacers and/or the like. The membranesupport structures 414 include openings 416 therethrough that allow thetransfer of heat and moisture between the liquid desiccant and the airstream 332.

The liquid-side structural spacers 418 and 424 are positioned around theliquid-desiccant flow guide screen 410. The spacers separate the twomembranes 412 that are bonded onto each side of the spacers 418 and 424.The membranes 412 are coupled to the diffuser spacers 418 to form a gapor liquid-flow channel between each membrane 412. Ends 424 and 420 formthe air-flow entrance and exit supports of the liquid flow panel 334. Atop 422 of one liquid-flow channel spacer 418 forms a portion of the topsupport 370 of the liquid-flow panel 334. A bottom 424 of the otherliquid-flow channel spacer 418 forms a portion of the bottom support 372of the liquid-flow panel 334. The top support 370 and the bottom support372 are also formed by air channel spacers 426. The air channel spacers426 are configured to abut the air channel spacers 426 of an adjacentpanel 334. The air channel spacers 426 form an air-flow gap betweenadjacent liquid-flow panels 334. The air-flow gaps between adjacentliquid-flow panels 334 form the air channels 336 within the energyexchange cavity.

FIG. 6 a illustrates an air channel 336 formed between adjacentmembranes for liquid-flow panels 334. The air channel 336 is configuredto carry the air stream 332 therethrough. The air channel 336 isdesigned to have a uniform width 430 along a length 432 of the airchannel 336. However, due to elastic deformations of the membranesupport structures 414 of the panel 334, there may be significantvariations in the air channel width. The air-side membrane supportstructures 414 limits the amount of membrane deflection restricting theair flow channel width that is caused by the difference in staticpressure in the liquid channel 334 and air channel 332. For example, themembrane support structures 414 limit the amount of deflection oversmall fraction, but a finite region, of each membrane. With respect tofactor G4, the air and liquid flow channel statistical variations fortypical individual flow tube hydraulic diameter variations may limited.With respect to factor G3, the average channel widths statisticalvariations for each fluid, among all the channels in the LAMER, may belimited.

FIG. 6 b illustrates an air-flow channel 336 that has been deformed byliquid air static pressure difference between adjacent liquid-flow andair-flow channels for a small finite region of the air-flow panel 334.Statistical variations in the deflections in the membrane air-flow andliquid flow channels can be deduced using mass or volume of liquid inthe LAMEE under typical liquid pressures measurements, carefullydeveloped pressure drop measurements across flow channels for each fluidand optical laser beam measurements for the minimum air-flow channelwidths. The measurements can then be used along with other data for thedeterminations of the air and liquid channel average and standarddeviations of flow hydraulic diameters for each fluid, which may bespecified separately for the typical channel (factor G4) and the set ofchannels in each LAMEE (factor G3). The design and manufacturing qualitycontrol and operation of a LAMEE may depend in part on knowing the data.

FIG. 7 is a graph 450 showing simulation results for optimum thermalcapacity rate ratio as a parameter on a chart of air humidity ratioversus air temperature for a passive RAMEE system, at steady-stateoperating conditions with the assumed indoor air at a wide range ofoutdoor air conditions. The graph 450 presents the optimum value of thethermal capacity rate ratio lines 452 that should be selected formaximum energy transfer effectiveness of the passive RAMEE system withtwo identical LAMEE units subject to the assumed constraints with eachand every air channel with a uniform width of 4.4 mm (with no internalsupport structure) and liquid-desiccant channel with a uniform width of2.7 mm (also with no internal structure), a membrane water vaporpermeability of 1.66E-6 kg/(m*s), and with fully developed laminar airand liquid flow in each channel. For different operating conditions andgeometric ratios graph 450 would have different values for the optimumvalue of Cr*, as described below.

The results for the optimum thermal capacity rate ratio with the assumedconstant widths of the air and liquid-desiccant channels and fullydeveloped laminar flow for each fluid is exemplary of one theoreticalcase only that differs significantly from what is physically possible.Although variable channel widths and turbulent channel flows are likelyto occur, presenting similar results for these cases would be much morecomplex; but, it can be done using the same computational procedures. Insuch cases, the optimum thermal capacity rate ratios will be verydifferent than those presented in graph 450 for the same outdoor airconditions.

Using graph 450 as an exemplary illustration of the design andoperational procedure to obtain the optimum steady-state effectiveness(and energy transfer rate) of a passive RAMEE system with two identicalLAMEEs each subject to the same mass flow rate of air, the systemoperator or automatic controller selects or controls the pumping rate ofthe liquid desiccant based on the outdoor air conditions of temperatureand humidity. That is, the optimum thermal capacity rate ratio 452 forthe particular outdoor air condition is selected to compute the massflow rate of liquid desiccant knowing the mass flow rate of air. Theresult is used to set the optimum pumping rate. When the outdoor airconditions change significantly or the air flow rate is changedsignificantly, a new optimum pumping rate is determined. In oneembodiment, the flow rate of the desiccant with respect to the flow rateof the air stream is controlled to achieve predetermined exchangerperformance ratios that at least partially define a sensible and latentenergy exchange between the desiccant and the air stream.

FIG. 8 is a graph 500 showing equilibrium, saturation, salt-solutionconcentration lines 502 superimposed on a psychrometric chart ofhumidity ratio versus temperature for several salts that may be used asliquid desiccants with the system 100. The graph 500 illustrates atemperature 504 of the air flowing through the LAMEE and a humidityratio 506 of the air at standard atmospheric pressure flowing throughthe LAMEE. The equilibrium, saturation, salt-solution concentrationlines 502 depend only on the type of salt, air temperatures 504 and thehumidity ratios 506 at which the desiccant will start to crystallizewithin the panels of the LAMEE. At the saturation concentration, aparticular salt solution will crystallize salt on the nearby membranesurfaces within the liquid-desiccant flow channel for any decrease inthe adjacent air flow channel temperature or humidity ratio (i.e. belowthe line 502 for the particular salt). Based on the expected conditionsfor a particular climatic region of the air flow through the LAMEE, thegraph 500 may be used along with other data to select an appropriatedesiccant for the air flow conditions for an HVAC application.

Line 508 represents the adjacent air temperatures 504 and humidityratios 506 at which a saturation magnesium chloride solutioncrystallizes if the air temperature and humidity were to drop below thisline. Line 510 represents the similar saturation calcium chloridesolution crystallization line. Line 512 represents the similarsaturation lithium iodide solution crystallization line. Line 514represents the similar saturation lithium chloride crystallization line.Line 516 represents the similar saturation lithium bromidecrystallization line.

Lithium bromide is capable of functioning as a liquid desiccant in theharshest conditions because only very low adjacent air humidity ratioswould cause crystallization. However, lithium bromide is relativelyexpensive in comparison to other salts with no lithium content. In anexemplary embodiment, the system 100 utilizes a desiccant mixture ofmagnesium chloride with other salts. The mixture may include magnesiumchloride and at least one of lithium chloride or lithium bromide.Alternatively, the mixture includes calcium chloride in place ofmagnesium chloride and at least one of lithium chloride or lithiumbromide. In another embodiment, the mixture includes at least three ofmagnesium chloride, calcium chloride, lithium chloride and/or lithiumbromide. The concentration of magnesium chloride can range from 0% to35.5% (i.e. saturation salt concentration). Above the saturation saltsolution line for a particular salt in graph 500, the equilibrium saltconcentration is based on a temperature and humidity of the air flowingthrough the LAMEE. A salt solution is comprised of water and ions ofsalts. The concentration of lithium chloride can range from 0% to 45.9%(i.e. saturation salt concentration). In one embodiment, the mixture is50% magnesium chloride and 50% lithium chloride. The mixture can operatewithout crystallization at temperatures 504 and humidity ratios 506below the line 508 for magnesium chloride. The mixture provides a liquiddesiccant that can operate at dryer air conditions for the outdoor airconditions for the RAMEE system than pure magnesium chloride or calciumchloride solutions.

In one embodiment, the desiccant is selected based on operational designparameters P10 and P11 as illustrated in Table 1. The desiccant may beselected based on a time duration (t_(salt,risk)) for a risk ofcrystallization in the desiccant over a typical year of weather data fora building located in a particular climate. In particular, the timeduration (t_(salt,risk)) for a risk of crystallization in the desiccantis divided by the total yearly time duration of system operation(t_(op)). In one embodiment, the parameter P10 is within a range oft_(salt,risk)/t_(op)<0.15. In another embodiment, the desiccant isselected based on a cost of salt or mixture of salts used in the RAMEEsystem 100 divided by the corresponding cost of LiCl for the system(C_(salt,mix)/CLiCl). In one embodiment, the parameter P11 is within arange of C_(salt,mix)/CLiCl<1. The parameters P10 and P11 may beindividually selected in part to achieve a predetermined performance ofthe LAMEE 300 and the RAMEE system 100. In another embodiment, both ofthe design parameters P10 and P11 may be utilized to achieve thepredetermined performance.

The geometric design and operating factors G1 to G8 and the physicaloperational and design factors P1 to P12 shown in Table 1 are selectedto achieve a predetermined performance of the LAMEE 300 and/or the RAMEEsystem 100. The geometric factors G1-G10 and the physical factors P1-P12may each be selected to achieve the predetermined performance of theLAMEE 300 and/or the RAMEE system 100. In another embodiment, at leastsome of the factors G1-G10 and P1-P12 may be selected to achieve thepredetermined performance of the LAMEE 300 and the RAMEE system 100.

When LAMEE devices are used in passive RAMEE systems for energyrecovery, the aforementioned performance factors are sufficient forapplications where the system operates at or near steady-state. When theLAMEE devices are installed in actively controlled RAMEE and HVACsystems for air conditioning supply air, most of the above describedLAMEE performance factors still apply; however, the HVAC systemperformance may be characterized using different dimensionless ratios.For the purpose a coefficient of performance (COP) or energy efficiencyratio (EER) can be used for any typical steady-state orquasi-steady-state operating condition of the controlled RAMEE systemand the ratios can be modified for the annual integrated time averagevalues called seasonal energy efficiency ratio (SEER) for both theheating and cooling of a building located in a particular city. The COPor EER for the HVAC system is defined as the useful energy rate changeof the supply air from inlet to discharge conditions divided by all theauxiliary energy rate inputs to the HVAC system. Data for thecalculation of COP or EER could be measured occasionally orcontinuously.

Because the cost of auxiliary energy is usually very different forcooling and heating, the ratios should be treated separately. The SEERvalue for cooling the supply air in summer may be listed separate fromthe SEER value for heating supply air in winter. Since both heating andcooling are used with mechanical cooling and desiccant dehumidificationsystems, both forms of input energy may be used for the summeroperations. To obtain a high SEER for the HVAC system in a building,waste energy from exhaust air or other process sources can be useddirectly to condition or partly condition the supply air using RAMEEsystems or indirectly using heat pumps (and/or refrigerators) withambient air or ground water as the energy sources. The use of aneconomizer by-pass may also raise the SEER.

When modified RAMEE systems are used over the year in both active andpassive modes, the calculation of the SEER values for the HVAC systemshould account for the changes of mode as well as any extra energy usefor all the energy recovery or pumped energy.

From the above discussion of active HVAC system options, it is evidentthat claims for high SEER values are likely to change significantly forthe same or different buildings in different climates. Comparisons ofthe dimensionless performance ratios for actively controlled modifiedRAMEE systems within an HVAC system may be done with software to showthe life-cycle cost savings and the payback period for a particulardesign in a particular climate. Passive performance of a RAMEE system isstill very useful because it will vary directly with cost savings forenergy recovery and it can provide the best quantifiable proof ofperformance for both the RAMEE system and its two LAMEEs. As well, thepassive performance should be used directly for the estimation of theHVAC system performance, with a heat pump assisted RAMEE system and itscost savings.

FIG. 9 illustrates a LAMEE 200 formed in accordance with an alternativeembodiment. The LAMEE 200 may be used as the supply air LAMEE 108 and/orthe return air LAMEE 120 (shown in FIG. 1). The LAMEE 200 includes ahousing 202 having a body 204. The body 204 includes a front 206 and aback 208 opposite the front 206. The body 204 is elongated to extendalong a length 210 between the front 206 and the back 208. The body 204includes a top 212 and a bottom 214 that are parallel to one another.The body 204 includes a height 216 that extends between the top 212 andthe bottom 214. The body 204 includes a first side 218 and a second side220. The first side 218 and the second side 220 span the length 210between the front 206 and the back 208. The first side 218 and thesecond side 220 span the height 216 between the top 212 and the bottom214. The first side 218 and the second side 220 are arranged parallel toone another and are separate by a width 222.

The LAMEE body 204 includes an air inlet 205 at the front 206 of thebody 204 and an air outlet 207 at the back 208 of the body 204. TheLAMEE body 204 forms an energy exchange cavity 224. The energy exchangecavity 224 extends the length 210, height 216, and width 222 between thefront 206, the back 208, the top 212, the bottom 214, the first side218, and the second side 220. The length 210, height 216, and/or width222 represent physical design factors that are selected to satisfypredetermined ratios with one another and/or with predetermined ratioswith other design parameters, as explained hereafter. The ratios of theheight 216 to the length 210, the width 222 to the length 210, and/orthe width 222 to the height 216 represent dimensionless physical ratios,and more generally, dimensionless design factors.

The energy exchange cavity 224 includes a plurality of energy exchangepanels 226 extending therethrough. The panels 226 extend the length 210and height 216 of the energy exchange cavity 224. Each panel 226 forms adesiccant channel that carries desiccant 241 through the energy exchangecavity 224. The panels 226 are arranged parallel to one another andspaced apart to form air channels 230 and desiccant channels 231therebetween. The air channels 230 extend between the air inlet 205 andthe air outlet 207. Each air channel 230 is formed between adjacentdesiccant channels 231. The air channels 230 direct an air stream 234from the front 206 of the LAMEE 200 to the back 208 of the LAMEE 200.

A desiccant inlet housing 236 is joined to the LAMEE housing 202. In theillustrated embodiment, the desiccant inlet housing 236 is joined to thebottom 214 of the LAMEE housing 202. The desiccant inlet housing 236 ispositioned adjacent the back 208 of the LAMEE housing 202. The desiccantinlet housing 236 extends from the back 208 of the LAMEE housing 202along the bottom 214 of the LAMEE housing 202. The desiccant inlethousing 236 extends partially between the back 208 and front 206 of theLAMEE housing 202. Alternatively, the desiccant inlet housing 236 maypositioned at any location along the LAMME body 204. In one embodiment,the LAMEE 200 may include more than one desiccant inlet body 204. Thedesiccant inlet housing 236 extends a length 238 along the bottom 214 ofthe LAMEE housing 202. The length 238 that the desiccant inlet housing236 extends is based on a predetermined performance of the LAMEE 200. Inone embodiment, the desiccant inlet housing 202 extends no more than onefourth of the length 210 of the LAMEE body 204. In another embodiment,the desiccant inlet housing 236 extends one fifth of the length 210 ofthe LAMEE body 204.

The desiccant inlet housing 236 includes an inlet 240 and an outlet 242.The inlet 240 is configured to receive desiccant 241 from a storage tank128 (shown in FIG. 1). The inlet 240 and the outlet 242 are in fluidcommunication with the desiccant channels 231 extending through theenergy exchange cavity 224. The desiccant 241 flows from the desiccantinlet housing 236 into the desiccant channels 231. The desiccant 241flows through the desiccant channels 231 from the back 208 of the LAMEEhousing 202 toward the front 206 of the LAMEE housing 202. The desiccant241 flows in a direction opposite the direction of the air stream 234.The desiccant 241 flows through the desiccant channels 231 toward adesiccant outlet housing 244.

The desiccant outlet housing 244 is joined to the top 212 of the LAMEEhousing 202. The desiccant outlet housing 244 is positioned proximate tothe front 206 of the LAMEE housing 202. Alternatively, the desiccantoutlet housing 244 may be positioned at any location along the top 212of the LAMEE housing 202. The desiccant outlet housing 244 is offsetfrom the desiccant inlet housing 236 along the direction of the airstream 234. The desiccant outlet housing 244 extends from the front 206of the LAMEE housing 202 along the top 212 of the LAMEE housing 202. Thedesiccant outlet housing 244 extends partially between the front 206 andthe back 208 of the LAMEE housing 202. The desiccant outlet housing 244extends a length 246 along the top 212 of the LAMEE housing 202. Thelength 246 that the desiccant outlet housing 244 extends is based on apredetermined performance of the LAMEE 200. In one embodiment, thedesiccant outlet housing 244 extends a length 246 that is no more thanone fifth the channel energy exchange length 210 of the LAMEE body 204.In one embodiment, the desiccant outlet housing 244 extends a length 246that is one fifth of the length 210 of the LAMEE body 204.

The desiccant outlet housing 244 includes an inlet 248 and an outlet250. The inlet 248 is in fluid communication with the desiccant channels231. The desiccant outlet housing 244 receives desiccant 241 from thedesiccant channels 231. The desiccant outlet housing 244 channels thedesiccant 241 through the outlet 250. The outlet 250 is in fluidcommunication with a storage tank 128 (shown in FIG. 1).

The desiccant inlet housing 236 and the desiccant outlet housing 244form a non-linear desiccant flow path 252 through the panels 226. Thedesiccant flow path 252 flows in a direction opposite to the air stream234. The desiccant flow path 252 travels upstream with respect to thedirection of the air stream 234. The desiccant flow path 252 is across/counter flow path with respect to the air stream 234 flowingthrough the air channels 230. An inlet cross segment 254 of thedesiccant flow path 252 is formed as the desiccant 241 enters the panels226 from the desiccant inlet housing 236. Desiccant 241 flowing from thedesiccant inlet housing 236 into the panels 226 flows upward through theinlet cross segment 254. Desiccant in the inlet cross segment 254 flowsin a cross flow arrangement that is substantially perpendicular to thedirection of the air stream 234.

As the desiccant 241 is channeled from the desiccant inlet housing 236fills the panels 226, the desiccant 241 begins flowing through a countersegment 256 of the desiccant flow path 252. The counter segment 256extends a length 258 through the panels 226. The length 258 is based ona predetermined performance of the LAMEE 200. The counter segment 256flows in a counter flow arrangement with respect to the direction of theair stream 234 flowing through the air channels 230. The counter segment256 flows substantially parallel to the direction of the air stream 234.The counter segment 256 flows upstream with respect to the direction ofthe air stream 234. The counter flow arrangement provides apredetermined heat and moisture exchange between the desiccant in thepanels 226 and the air stream 234 in the air channels 230.

The desiccant 241 in the counter segment 256 flows into an outlet crosssegment 260 of the desiccant flow path 252. The outer cross segment 260flows substantially perpendicular to the direction of the air stream234. The desiccant in the outlet cross segment 260 flows in a cross flowarrangement with respect to the air 234 in the air channels 230. Thedesiccant in the outlet cross segment 260 flows upward from the countersegment 256 to the desiccant outlet housing 244.

The cross/counter flow arrangement of the desiccant flow path 252provides desiccant counter flow with respect to the direction of the airstream 234. The counter flow arrangement improves an efficiency of theLAMEE 200. The cross/counter flow arrangement does not require largeheaders that would otherwise increase the space required for the LAMEE200. The illustrated embodiment shows the desiccant flow path 252flowing upward from the bottom 214 of the LAMEE 200 to the top 212 ofthe LAMEE 200. Optionally, the desiccant inlet housing 236 may bepositioned on the top 212 of the LAMEE 200 and the desiccant outlethousing 244 may be positioned on the bottom 214 of the LAMEE 200. Insuch an embodiment, the desiccant flow path 252 may flow downward fromthe top 212 of the LAMEE 200 to the bottom 214 of the LAMEE 200.

The geometric design factors G1-G8 and the physical operational anddesign factors P1-P12 shown in Table 1 should be used to achieve apredetermined performance of the LAMEE 200. Although each of thedimensionless independent factors in the set, G1-G10 and P1-P12, shouldbe selected within the specified ranges in Table 1 to achieve thepredetermined performance of the passive RAMEE system with its two LAMEE200 units operating at steady-state, it may be possible to relax thedesign and operational range of a few independent factors in Table 1 forsome narrow range of system operating conditions and still achieve anacceptable system performance. Therefore, in another embodiment, onlysome of the factors, G1-G10 and P1-P12, need to be selected in theranges specified in Table 1 to achieve an acceptable predeterminedperformance of the LAMEE 200 when tested as part of a passive RAMEEsystem.

FIG. 10 illustrates a LAMEE 600 formed in accordance with an alternativeembodiment. The LAMEE 600 includes a housing 602 having a body 604 witha top 606 and a bottom 608. The LAMEE 600 includes an air inlet 610 andan air outlet 612. An energy exchange cavity 614 extends through thebody 604 between the air inlet 610 and the air outlet 612. An air stream616 flows through the energy exchange cavity 614 from the air inlet 610to the air outlet 612. The energy exchange cavity 614 includes panels618 that form desiccant channels 615 to carry desiccant therethrough.

A desiccant inlet 620 is provided at the bottom 608 of the LAMEE body604. The desiccant inlet 620 may be positioned at any location along thebottom 608 of the LAMEE body 604. Alternatively, the LAMEE 600 mayinclude any number of desiccant inlets 620. The desiccant inlet 620 isin flow communication with the desiccant channels 615. A first desiccantoutlet 622 and a second desiccant outlet 624 are positioned at the top606 of the LAMEE body 604. The first and second desiccant outlets 622and 624 may be positioned at any location along the top 606 of the LAMEEbody 604. The first and second desiccant outlets 622 and 624 are offsetfrom the desiccant inlet 620 along the direction of the air stream 616.The desiccant inlet 620 and the desiccant outlets 622 and 624 fromdesiccant flow paths from the bottom 608 of the LAMME body 604 to thetop 606 of the LAMEE body 604. Alternatively, the desiccant inlet 620may be positioned along the top 606 of the LAMEE body 604 and thedesiccant outlets 622 and 624 may be positioned along the bottom 608 ofthe LAMEE body 604. In such an embodiment, the desiccant flows from thetop 606 of the LAMEE body 604 to the bottom 608 of the LAMEE body 604.

The desiccant inlet 620 and the first desiccant outlet 622 form a firstdesiccant flow path 626 that flows non-linearly through the panels 618.The first desiccant flow path 626 includes an inlet segment 628 thatflow from the desiccant inlet 620. The inlet segment 628 flows in across flow direction substantially perpendicular to the direction of theair stream 616. The inlet segment 628 flow into an intermediate segment630 that flows substantially parallel to the direction of the air stream616. The intermediate segment 630 flows in the same direction as thedirection of the air stream 616. The intermediate segment 630 flows intoan outlet segment 632 that flows to the desiccant outlet 622. The outletsegment 632 flows in a direction that is substantially perpendicular tothe direction of the air stream 616.

The desiccant inlet 620 and the second desiccant outlet 624 form asecond desiccant flow path 634 that flows non-linearly through thepanels 618. The second desiccant flow path 634 includes an inlet segment636 that flows from the desiccant inlet 620. The inlet segment 636 flowsin a cross flow direction substantially perpendicular to the directionof the air stream 616. The inlet segment 636 flows into an intermediatesegment 638 that flows substantially parallel to the direction of theair stream 616. The intermediate segment 638 flows in an oppositedirection to the direction of the air stream 616. The intermediatesegment 638 flows into an outlet segment 640 that flows to the seconddesiccant outlet 624. The outlet segment 640 flows in a direction thatis substantially perpendicular to the direction of the air stream 616.

The physical design geometric factors G1-G10 and the operational designfactors P1-P12 shown in Table 1 may be used to achieve a predeterminedperformance of the LAMEE 600. The physical design geometric factorsG1-G10 and the operational design factors P1-P12 may each be selected toachieve the predetermined performance of the LAMEE 600. In anotherembodiment, only some of the physical design geometric factors G1-G10and the operational design factors P1-P12 may be selected to achieve thepredetermined performance of the LAMEE 600.

FIG. 11 illustrates a LAMEE 650 formed in accordance with an alternativeembodiment. The LAMEE 650 includes a housing 652 having a body 654 witha top 656 and a bottom 658. The LAMEE 650 includes an air inlet 660 andan air outlet 662. An energy exchange cavity 664 extends through thebody 654 between the air inlet 660 and the air outlet 662. An air stream666 flows through the energy exchange cavity 664 from the air inlet 660to the air outlet 662. The energy exchange cavity 664 includes panels668 that form desiccant channels 669 to carry a desiccant therethrough.

A desiccant outlet 670 is provided at the top 656 of the LAMER body 654.The desiccant outlet 670 may be positioned at any location along the top656 of the LAMEE body 654. Alternatively, the LAMEE 650 may include anynumber of desiccant outlets 670. The desiccant outlet 670 is in flowcommunication with the desiccant channels 669. A first desiccant inlet672 and a second desiccant inlet 674 are positioned at the bottom 658 ofthe LAMEE body 654. The first and second desiccant inlets 672 and 674may be positioned at any location along the bottom 658 of the LAMEE body654. The first and second desiccant inlets 672 and 674 are offset fromthe desiccant outlet 670 along the direction of the air stream 666. Thedesiccant outlet 670 and the desiccant inlets 672 and 674 form desiccantflow paths from the bottom 658 of the LAMME body 654 to the top 656 ofthe LAMER body 654. Alternatively, the desiccant outlet 670 may bepositioned along the bottom 658 of the LAMEE body 654 and the desiccantinlets 672 and 674 may be positioned along the top 656 of the LAMEE body654. In such an embodiment, the desiccant flows from the top 656 of theLAMER body 654 to the bottom 658 of the LAMEE body 654.

The desiccant outlet 670 and the first desiccant inlet 672 form a firstdesiccant flow path 676 that flows non-linearly through the panels 668.The first desiccant flow path 676 includes an inlet segment 678 thatflow from the first desiccant inlet 672. The inlet segment 678 flows ina cross flow direction substantially perpendicular to the direction ofthe air stream 666. The inlet segment 678 flows into an intermediatesegment 680 that flows substantially parallel to the direction of theair stream 666. The intermediate segment 680 flows in a directionopposite to the direction of the air stream 666. The intermediatesegment 680 flows into an outlet segment 682 that flows to the desiccantoutlet 670. The outlet segment 682 flows in a direction that issubstantially perpendicular to the direction of the air stream 666.

The desiccant outlet 670 and the second desiccant inlet 674 form asecond desiccant flow path 684 that flows non-linearly through thepanels 668. The second desiccant flow path 684 includes an inlet segment686 that flows from the first desiccant inlet 674. The inlet segment 686flows in a cross flow direction substantially perpendicular to thedirection of the air stream 666. The inlet segment 686 flows into anintermediate segment 688 that flows substantially parallel to thedirection of the air stream 666. The intermediate segment 688 flows inthe same direction as the direction of the air stream 666. Theintermediate segment 688 flows into an outlet segment 690 that flows tothe desiccant outlet 670. The outlet segment 690 flows in a directionthat is substantially perpendicular to the direction of the air stream666.

The physical design geometric factors G1-G10 and the operational designfactors P1-P12 shown in Table 1 may be used to achieve a predeterminedperformance of the LAMEE 650. The physical design geometric factorsG1-G10 and the operational design factors P1-P12 may each be selected toachieve the predetermined performance of the LAMEE 650. In anotherembodiment, only some of the physical design geometric factors G1-G 10and the operational design factors P1-P12 may be selected to achieve thepredetermined performance of the LAMEE 650.

FIG. 12 illustrates a LAMEE 700 formed in accordance with an alternativeembodiment. The LAMEE 700 includes a housing 702 having a body 704 witha top 706 and a bottom 708. The LAMEE 700 includes a first end 710 and asecond end 712. An energy exchange cavity 714 extends through the body704 between the first end 710 and the second end 712. An air stream 716flows through the energy exchange cavity 714 from the first end 710 tothe second end 712. The energy exchange cavity 714 includes panels 718that form desiccant channels 719 to carry a desiccant therethrough.

A desiccant flow path 726 flows through the desiccant channels 719 fromthe second end 712 to the first end 710. The desiccant flow path 726 isarranged in a counter-flow arrangement with respect to the air stream716. Heat is transferred through the panels 719 between the desiccantflow path 726 and the air stream 716.

The physical design geometric factors G1-G10 and the operational designfactors P1-P12 shown in Table 1 may be used to achieve a predeterminedperformance of the LAMEE 700. The physical design geometric factorsG1-G10 and the operational design factors P1-P12 may each be selected toachieve the predetermined performance of the LAMEE 700. In anotherembodiment, only some of the physical design geometric factors G1-G10and the operational design factors P1-P12 may be selected to achieve thepredetermined performance of the LAMEE 700.

FIG. 13 illustrates a LAMEE 750 formed in accordance with an alternativeembodiment. The LAMEE 750 includes a housing 752 having a body 754 witha top 756 and a bottom 758. The LAMEE 750 includes a first end 760 and asecond end 762. An energy exchange cavity 764 extends through the body754 between the first end 760 and the second end 762. An air stream 766flows through the energy exchange cavity 764 from the first end 760 tothe second end 762. The energy exchange cavity 764 includes panels 768that form desiccant channels to carry a desiccant therethrough.

A desiccant flow path 776 flows through the desiccant channels from thetop 756 to the bottom 758. The desiccant flow path 776 is arranged in across-flow arrangement with respect to the air stream 766. Heat istransferred through the panels 768 between the desiccant flow path 776and the air stream 766.

The physical design geometric factors G1-G10 and the operational designfactors P1-P12 shown in Table 1 may be used to achieve a predeterminedperformance of the LAMEE 750. The physical design geometric factorsG1-G10 and the operational design factors P1-P12 may each be selected toachieve the predetermined performance of the LAMEE 750. In anotherembodiment, only some of the physical design geometric factors G1-G10and the operational design factors P1-P12 may be selected to achieve thepredetermined performance of the LAMEE 750.

FIG. 14 illustrates an exemplary energy exchange system 850 formed inaccordance with the set of embodiments specified in Table 1. The energyexchange system 850 is configured to condition air supplied to anenclosed structure 852 having a plurality of rooms 854. The energyexchange system 850 receives pre-conditioned air 856 that is directthrough the system 850 with a fan 858. The pre-conditioned air 856 isdirected to a supply LAMEE 860 that conditions the pre-conditioned air856 to generate supply air 862. The supply LAMEE 860 conditions thepre-conditioned air 856 by adding or removing heat and moisture to orfrom the pre-conditioned air 856. The supply air 862 is discharged intothe rooms 854.

Each room 854 includes a return air LAMEE 864 configured to receivereturn air 866 from the room 854. The return air LAMEE 864 conditionsthe return air 866 by adding or removing heat and moisture to or fromthe return air 866. The return air LAMEEs 864 exchange the heat andmoisture with the supply air LAMEE 860 to transfer the heat and moisturebetween the return air 866 and the pre-conditioned air 856. The returnLAMEEs 864 generate exhaust air 868 that is discharged from the energyexchange system 850 by a fan 870.

Liquid desiccant 872 flows between the supply LAMEE 860 and the returnair LAMEEs 864. The desiccant 872 transfers the heat and moisturebetween the supply LAMEE 860 and the return air LAMEEs 864. Storagetanks 874 are provided to retain the desiccant 872 as it flows betweenthe supply LAMEE 860 and the return air LAMEEs 864. Pumps 876 may beprovided to move the liquid desiccant 872 between the supply LAMEE 860and the return air LAMEEs 864.

FIG. 15 illustrates an alternative exemplary energy exchange system 900formed in accordance with the set of embodiments. The energy exchangesystem 900 is configured to condition air supplied to a structure 901.The structure 901 includes a plurality of rooms 903. The energy exchangesystem 900 includes an inlet 902 that receives pre-conditioned air 904that may be moved by a fan 905. The pre-conditioned air 904 is dividedinto each of the rooms 903 of the structure 901. The pre-conditioned air904 is moved through the energy exchange system 900 with a fan 905. Thepre-conditioned air 904 may be divided equally between each of the rooms903. Optionally, the pre-conditioned air 904 may be divided between therooms 903 based on a capacity of each room 903 and/or a supply air needin each room 903. Each room 903 includes a supply LAMEE 906 that isconfigured to condition the pre-conditioned air 904. The supply LAMEE906 conditions the per-conditioned air by adding or removing heat andmoisture to the pre-conditioned air 904. The supply LAMEE 906 generatessupply air 908 that is discharged into the room 903.

Return air 910 from each room 903 is channeled to a return LAMEE 912.The return LAMEE 912 conditions the return air 910 to generate exhaustair 915. The exhaust air 915 is moved through the energy exchange system900 with a fan 907 that directs the exhaust air 915 to an outlet 909.The return LAMEE 912 conditions the return air 910 by adding or removingheat and moisture from the return air 910. Heat and moisture istransferred between the supply LAMEE 906 and the return LAMEE 912 toexchange the heat and moisture between the return air 910 and thepre-conditioned air 904.

Desiccant 914 flows between the supply LAMEE 906 and the return LAMEE912. The desiccant 914 transfers the heat and moisture between thesupply LAMEE 906 and the return LAMEE 912. Storage tanks 916 areprovided between the supply LAMEE 906 and the return LAMEE 912. Thestorage tanks 916 retain desiccant traveling between the supply LAMEE906 and the return LAMEE 912. Pumps 918 are provided to move thedesiccant 914 between the supply LAMEE 906 and the return LAMEE 912.

In another embodiment, an energy exchange system may be provided thatincludes individual supply LAMEEs and return LAMEEs for each room of astructure. Alternatively, an energy exchange system may be provided thatutilizes heat and moisture from a first room of a structure to conditionair in a second room of the structure. Such an embodiment would includea first LAMEE positioned within the first room and a second LAMEEpositioned within the second room. The heat and moisture from the firstroom would be transferred from the first LAMEE to the second LAMEE toadd the heat and moisture to the air in the second room.

The embodiments described herein provide a LAMEE that utilizes either acounter/cross-flow or cross-flow to improve the effectiveness of theLAMEE. The dimensions of the LAMEE are selected to provide apredetermined performance of the LAMEE. The predetermined performance ofthe LAMEE is based on the surrounding environment. The LAMEE isconfigured to reach the predetermined performance based on theconditions of the air flow through the LAMEE. The embodiments hereinalso provide a desiccant solution that is configured to operate at dryambient air conditions.

It should be noted that the LAMEEs illustrated in FIGS. 2 and 9-13 areexemplary only and the physical design geometric factors G1-G10 and theoperational design factors P1-P12 may be utilized with any LAMEE havingany suitable geometry. Further, the energy exchange systems illustratedin FIGS. 14 and 15 are exemplary only and the physical design geometricfactors G1-G10 and the operational design factors P1-P12 may be utilizedwith any suitable energy exchange system.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the variousembodiments of the invention without departing from their scope. Whilethe dimensions and types of materials described herein are intended todefine the parameters of the various embodiments of the invention, theembodiments are by no means limiting and are exemplary embodiments. Manyother embodiments will be apparent to those of skill in the art uponreviewing the above description. The scope of the various embodiments ofthe invention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Moreover, in the following claims, theterms “first,” “second,” and “third,” etc. are used merely as labels,and are not intended to impose numerical requirements on their objects.Further, the limitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. §112, sixth paragraph, unless and until such claimlimitations expressly use the phrase “means for” followed by a statementof function void of further structure.

This written description uses examples to disclose the variousembodiments of the invention, including the best mode, and also toenable any person skilled in the art to practice the various embodimentsof the invention, including making and using any devices or systems andperforming any incorporated methods. The patentable scope of the variousembodiments of the invention is defined by the claims, and may includeother examples that occur to those skilled in the art. Such otherexamples are intended to be within the scope of the claims if theexamples have structural elements that do not differ from the literallanguage of the claims, or if the examples include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

What is claimed is:
 1. An energy exchanger comprising: a housingconstructed to meet a predetermined exchanger aspect ratio; a pluralityof panels extending through the housing, the panels having asemi-permeable membrane forming an energy exchange area of the panel,the panels forming desiccant channels and air channels that areseparated by the semi-permeable membranes to facilitate contact betweenan air stream flowing through the air channels and desiccant flowingthrough the desiccant channels within the energy exchange areas of thepanels, the energy exchange area of each panel having a top and abottom, a height of the energy exchange area defined between the top andthe bottom, the energy exchange area of each panel having a front and aback, a length of the energy exchange area defined between the front andthe back, the exchanger aspect ratio being defined by the height of theenergy exchange area of each panel divided by the length of the energyexchange area of each panel; a desiccant inlet in flow communicationwith the desiccant channels; and a desiccant outlet in flowcommunication with the desiccant channels, the desiccant channelsconfigured to channel the desiccant from the desiccant inlet to thedesiccant outlet in at least one of a counter-flow or cross-flowdirection with respect to the direction of the air stream to facilitateheat and water vapor transfer through the semi-permeable membranes, theexchanger aspect ratio selected to provide at least one of apredetermined membrane area, a predetermined length, or a predeterminedduration of exposure of the air stream to the desiccant.
 2. The energyexchanger of claim 1, wherein the exchanger aspect ratio is within arange of 0.5 to
 2. 3. The energy exchanger of claim 1, wherein thedesiccant inlet is offset from the desiccant outlet along the directionof the air stream.
 4. The energy exchanger of claim 1, wherein thedesiccant flows through the desiccant channels along a non-linear flowpath between the inlet and outlet.
 5. The energy exchanger of claim 1,wherein the desiccant flows through the desiccant channels along a flowpath, the flow path having a cross-flow segment and a counter-flowsegment, the cross-flow segment extending in a flow directionsubstantially perpendicular to the flow direction of the air stream, thecounter-flow segment extending in a direction approximately 180° fromthe flow direction of the air stream.
 6. The energy exchanger of claim1, wherein the desiccant flows along a flow path in a flow directionthat is at least partially counter-flow with respect to the flowdirection of the air stream.
 7. The energy exchanger of claim 1, whereina flow rate of the desiccant with respect to a flow rate of the airstream is controlled to achieve predetermined exchanger performanceratios that at least partially define a sensible and latent energyexchange between the desiccant and the air stream.
 8. The energyexchanger of claim 1, wherein the semi-permeable membrane is selectedbased on at least one of a water vapor transfer resistance ratio, aliquid break through pressure ratio, or an elastic tensile yield limitratio of the membrane.
 9. The energy exchanger of claim 1, wherein theplurality of panels include support structures to limit deformation ofthe panel membrane.
 10. The energy exchanger of claim 1, wherein acharacteristic Reynolds number for the air stream through the airchannels is greater than a critical Reynolds number for turbulent flowin the air channels.
 11. The energy exchanger of claim 1, wherein theair channels include turbulence enhancing surface roughness features tofacilitate increasing energy transfer that exceeds an additional airpressure drop energy loss when convective heat and latent energytransfer increase.
 12. The energy exchanger of claim 1, wherein acharacteristic Rayleigh number for desiccant flow in the desiccantchannels is less than a critical Rayleigh number for thermally inducedliquid density instability causing non-uniform mal-distributed flow at aReynolds number for desiccant flow.
 13. The energy exchanger of claim 1,wherein desiccant channels include turbulence enhancing surfaceroughness features when a Rayleigh number is less than a criticalRayleigh number at a Reynolds number for the flow.
 14. The energyexchanger of claim 1, wherein a thermal insulation surrounding thepanels is such that a heat exchange rate between the panels is less than5% of a heat rate between supply and exhaust air flow streams during astandard summer or winter test with AHRI 1060 air inlet operatingconditions.
 15. An energy exchanger comprising: a housing; a pluralityof panels forming desiccant channels air channels separated by at leastone semi-permeable membrane, the air channels configured to direct anair stream through the housing, the plurality of panels spaced apartbased on predetermined air to desiccant mass flow rates that define anair channel width and a desiccant channel width; a desiccant inlet inflow communication with the desiccant channels; and a desiccant outletin flow communication with the desiccant channels, the desiccantchannels configured to channel desiccant from the desiccant inlet to thedesiccant outlet in at least one of a counter-flow or cross-flowdirection with respect to the direction of the air stream to facilitateheat and water vapor transfer between the desiccant in the desiccantchannels and the air stream in the air channels, the air to desiccantmass flow rates selected to provide a predetermined mass or volume ofair stream flowing through the air channels or a predetermined mass orvolume of desiccant flowing through the desiccant channels.
 16. Theenergy exchanger of claim 15, wherein the desiccant channels have anapproximately constant desiccant channel width through the housing andthe air channels have an approximately constant air channel widththrough the housing.
 17. The energy exchanger of claim 15, wherein aratio of the average air channel width divided by the average desiccantchannel width is within a range of 1 to
 5. 18. An energy exchangercomprising: a housing; a plurality of panels forming desiccant channelsand air channels extending through the housing, the air channelsconfigured to direct an air stream through the housing; a desiccantinlet in flow communication with the desiccant channels; a desiccantoutlet in flow communication with the desiccant channels, the desiccantchannels configured to channel desiccant from the desiccant inlet to thedesiccant outlet in at least one of a counter-flow or cross-flowdirection with respect to the direction of the air stream; and asemi-permeable membrane extending through each panel to facilitate heatand water vapor transfer between the desiccant in the desiccant channelsand the air stream in the air channels, the air stream and the desiccantcausing the semi-permeable membrane to deflect during operation, thedesiccant membrane selected based on predetermined channel deflectionranges that are defined to limit the amount of membrane deflection. 19.The energy exchanger of claim 18, wherein a standard deviation of ahydraulic diameter of at least one of the air channels and desiccantchannels divided by a mean value of a hydraulic diameter for one of theair channels or desiccant channels is within a range 0.0 to 0.2.
 20. Theenergy exchanger of claim 18 further comprising: an air channel supportscreen having a solid area that is a fraction of a total area of the airchannel support screen; and a desiccant channel support screen having asolid area that is a fraction of a total area of the desiccant channelsupport screen.
 21. The energy exchanger of claim 18 further comprisingan air channel support screen, a distance between the air channelsupport screens in the flow direction of the air stream divided by adistance between the air channel support screens normal to flowdirection of the air steam is within a range of 0.01 to 5.0.
 22. Theenergy exchanger of claim 18, wherein an angle between a normal vectorto a plane of each air channel and desiccant channel and an accelerationof gravity vector is within a range of 45° to 135°.
 23. The energyexchanger of claim 18, wherein an angle between a vector parallel to alength of each panel and a vector direction of gravitationalacceleration is within a range of 60° to 120°.
 24. An energy exchangercomprising: a housing; a plurality of panels forming desiccant channelsseparated from air channels by at least one semi-permeable membrane, theair channels configured to direct an air stream through the housing; adesiccant inlet in flow communication with the desiccant channels; adesiccant outlet in flow communication with the desiccant channels, thedesiccant channels configured to channel desiccant from the desiccantinlet to the desiccant outlet in at least one of a counter-flow orcross-flow direction with respect to the direction of the air stream tofacilitate heat and water vapor transfer between the desiccant in thedesiccant channels and the air stream in the air channels, wherein thedesiccant is selected based on predetermined salt solution concentrationranges for a selected life span and cost of the desiccant.
 25. Theenergy exchanger of claim 24, wherein the time duration for a risk ofcrystallization in the desiccant flow channels over a year divided by atotal yearly time of energy exchanger operation is less than 0.15. 26.The energy exchanger of claim 24, wherein the cost of the desiccantdivided by the cost of a lithium chloride solution is less than
 1. 27.An energy exchanger comprising: a housing; a plurality of panels formingdesiccant channels extending through the housing, each of the pluralityof panels having a semi-permeable membrane that is selected to meetpredetermined membrane resistance ranges defining physical properties ofthe membrane; air channels formed between the desiccant channels, theair channels configured to direct an air stream through the housing; adesiccant inlet in flow communication with the desiccant channels; and adesiccant outlet in flow communication with the desiccant channels, thedesiccant channels configured to channel desiccant from the desiccantinlet to the desiccant outlet so that the semi-permeable membranesfacilitate heat and water vapor exchange between the desiccant and theair stream, the membrane resistance ranges selected to reduce flow ofthe desiccant through the semi-permeable membrane.
 28. The energyexchanger of claim 27, wherein the semi-permeable membrane has a watervapor diffusion resistance and the air stream in the air channel has aconvective water vapor mass transfer resistance, a ratio of the membranewater vapor transfer resistance divided by the convective water vapormass transfer resistance of the membrane is within a range of 0.2 to 3.29. The energy exchanger of claim 27, wherein the semi-permeablemembrane has a membrane liquid break-through pressure defined as thepressure required for desiccant to flow through the membrane, a ratio ofthe membrane liquid break-through pressure divided by (rho*g*H), whereinrho is the density of the desiccant, g is gravity and H is a height ofthe membrane, is greater than
 20. 30. The energy exchanger of claim 27,wherein the membrane has an edge seal liquid break-through pressuredefined as the pressure required for desiccant to flow through an edgeseal of the membrane, a ratio of the edge seal liquid break-throughpressure divided by (rho*g*H), wherein rho is the density of thedesiccant g is gravity and H is a height of the membrane, is greaterthan
 20. 31. The energy exchanger of claim 27, wherein the membraneincludes a screen having wires, the wires having a spacing (s_(ws)), thedesiccant having an operating pressure (p_(l,op)), and the membranehaving a tensile yield limit (T_(m,yl)), a ratio ofT_(m,yl)/(p_(l,op)*s_(w,s)) is less than 1.5.
 32. An energy exchangercomprising: a housing; a plurality of panels forming desiccant channelsextending through the housing, the plurality of panels each having asemi-permeable membrane; air channels formed between the desiccantchannels, the air channels configured to direct an air stream throughthe housing, the air stream flowing through the air channels at apredetermined air flow; a desiccant inlet in flow communication with thedesiccant channels; and a desiccant outlet in flow communication withthe desiccant channels, the desiccant channels configured to channeldesiccant from the desiccant inlet to the desiccant outlet so that thesemi-permeable membranes facilitate heat and water vapor exchangebetween the desiccant and air streams, the air flow of the air streamselected to meet a predetermined exposure of the air stream to thesemi-permeable membranes.
 33. The energy exchanger of claim 32, whereinan air flow pressure drop ratio is defined as (p_(h)A_(c)/V_(c)),wherein p_(h) is a pressure drop of the air stream across the energyexchanger, A_(c) is an area of an air channel, and V_(c) is a volume ofthe air channel, wherein the air flow pressure drop ratio is between1×10³ and 1×10⁴.
 34. An energy exchanger comprising: a housing; aplurality of panels forming desiccant channels extending through thehousing; air channels formed between adjacent desiccant channels, theair channels configured to direct an air stream through the housing; adesiccant inlet in flow communication with the desiccant channels; and adesiccant outlet in flow communication with the desiccant channels, thedesiccant channels configured to channel desiccant from the desiccantinlet to the desiccant outlet so that the semi-permeable membranesfacilitate heat exchange between the desiccant and the air stream,wherein the energy exchanger operates within predetermined exchangerperformance ratios that define a thermal and latent energy exchangebetween the desiccant and the air stream.
 35. The energy exchanger ofclaim 34, wherein an exchanger number of transfer units with the energyexchanger is within a range of 1 to
 15. 36. The energy exchanger ofclaim 34, wherein an exchanger thermal capacity rate ratio within theexchanger is within a range of 1 to
 10. 37. A method of exchangingenergy between a desiccant and an air stream, the method comprising:extending a plurality of panels through a housing of the energyexchanger to form desiccant channels and air channels; selecting asemi-permeable membrane for each of the panels; directing an air streamat a predetermined air mass flow ratio through the air channels; anddirecting desiccant through the desiccant channels, wherein thesemi-permeable membrane is selected based on membrane resistance rangesdefined to limit a flow of the desiccant through the desiccant membrane,the air flow ratio of the air stream is selected to meet a predeterminedexposure of the air stream to the desiccant membrane, and a flow rate ofthe desiccant with respect to a flow rate of the air stream iscontrolled to achieve predetermined exchanger performance ratios thatdefine a thermal energy exchange between the desiccant and the airstream.
 38. The method of claim 37, wherein an exchanger thermalcapacity rate ratio of the energy exchanger is within a range of 1 to10.
 39. The method of claim 37 wherein an exchanger number of transferunits with the energy exchanger is within a range of 1 to
 15. 40. Themethod of claim 37, wherein the membrane has a water vapor diffusionresistance and a convective water vapor mass transfer resistance in theair channel, a ratio of the membrane water vapor diffusion resistancedivided by the convective water vapor mass transfer resistance of themembrane is within a range of 0.2 to
 3. 41. The method of claim 37,wherein the membrane has a membrane liquid break-through pressuredefined as the pressure required for desiccant to flow through themembrane, a ratio of the membrane liquid break-through pressure dividedby (rho*g*H), wherein rho is the density of the desiccant, g is gravityand H is a height of the membrane, is greater than
 20. 42. The method ofclaim 37, wherein the membrane has an edge seal liquid break-throughpressure defined as the pressure required for desiccant to flow throughan edge seal of the membrane, a ratio of the edge seal liquidbreak-through pressure divided by (rho*g*H), wherein rho is the densityof the desiccant, g is gravity and H is a height of the membrane, isgreater than
 20. 43. The method of claim 37, wherein the membraneincludes a screen having wires, the wires having a spacing (s_(ws)), thedesiccant having an operating pressure (p_(l,op)), and the membranehaving a tensile yield limit (T_(m,yl)), a ratio ofT_(m,yl)/(p_(l,op)*s_(ws)) is less than 1.5.
 44. The method of claim 37,wherein the air flow resistance ratio is defined as (p_(h)A_(c)/V_(c)),wherein p_(h) is a pressure drop of the air stream across the energyexchanger, A_(c) is an area of an air channel, and V_(c) is a volume ofthe air channel, wherein the air flow resistance ratio is between 10³and 10⁴.
 45. The method of claim 37 further comprising controlling themass flow rate of the desiccant with respect to the mass flow rate ofthe air stream based on a temperature and humidity ratio of the airstream.
 46. The method of claim 37 further comprising controlling themass flow rate of the desiccant so that the thermal capacity rate ratioof the desiccant is no more than 5 times the thermal capacity rate ratioof the air stream.
 47. A method of exchanging energy between a desiccantand an air stream, the method comprising: extending a plurality ofpanels through a housing of the energy exchanger; spacing the pluralityof panels based on predetermined air to desiccant channel rates to formdesiccant channels and air channels between adjacent panels, thepredetermined air to desiccant channel rates defining an air channelwidth and a desiccant channel width; selecting a semi-permeable membraneto extend through the panels based on predetermined channel deflectionranges that are defined to limit an amount of membrane deflection;directing an air stream through the air channels; and directingdesiccant flow through the desiccant channels in at least one of acounter-flow or cross-flow direction with respect to the direction ofthe air stream so that the membrane facilitates heat and water vaporexchange between the desiccant in the desiccant channels and the airstream in the air channels, the predetermined air to desiccant channelrates providing a predetermined volume rate of air stream flowingthrough the air channels and a predetermined volume rate of desiccantflowing through the desiccant channels.
 48. The method of claim 47further comprising: providing a desiccant inlet in fluid communicationwith the desiccant channels; providing a desiccant outlet in fluidcommunication with the desiccant channels; and offsetting the desiccantinlet from the desiccant outlet along a direction of the air stream. 49.The method of claim 47 further comprising directing the desiccant alonga flow path having a cross segment and a counter segment, the crosssegment extending in a direction substantially perpendicular to adirection of the air stream, the counter segment extending in adirection substantially parallel to a direction of the air stream. 50.The method of claim 47 further comprising directing the desiccant alonga flow path in a direction upstream with respect to a direction of theair stream.
 51. The method of claim 47 further comprising controlling aflow rate of the desiccant with respect to a flow rate of the air streamto achieve predetermined exchanger performance ratios that define athermal energy exchange between the desiccant and the air stream.